This steak with cognac mushroom sauce pairs pan-seared beef with a glossy demi-glace sauce and garlic-parsley Parisian potatoes. The recipe works because the cognac is reduced before the demi-glace goes in, which keeps the sauce rounded rather than harsh. The main mistake is reducing too far: stop when the sauce coats a spoon in a thin, shiny layer.

This version is based on my YouTube video, with a few adjustments since publication to make the quantities and cooking times easier to reproduce at home. The original dish uses good marbled Angus steaks, mushrooms, shallots, cognac and a gelatin-rich veal demi-glace. I have kept that same bistro-style character while clarifying the strength of the demi-glace, the potato cooking time and the internal temperature of the steaks.

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What Makes This Recipe Different

This is not a creamy steak sauce. It is a darker, more concentrated pan sauce built with cognac and prepared demi-glace. The mushrooms absorb the browned flavour left in the skillet, while Dijon mustard brings enough sharpness to balance the richness without turning the dish into a mustard sauce.

For a softer and creamier variation, my Steak Diane with cognac and mushrooms goes in a different direction. This version is closer to a classic French brown sauce, with a glossy texture and a deeper roasted flavour. A good homemade brown sauce is also useful when prepared demi-glace is not available.

The Parisian potatoes make the plate feel more traditional than ordinary roasted potatoes. They are cut into small balls with a melon baller, briefly simmered and then browned in a skillet. The trimmings do not need to be wasted. Save them for soup, mashed potatoes or another potato dish.

This is a hearty, protein-rich meal with a rich sauce and buttery potatoes. It works for a cold-weather supper, a birthday dinner or a year-round bistro meal when you want something more involved than a basic grilled steak.

Ingredients You Need

Use three boneless steaks that are about 1 to 1¼ inches thick. Strip loin, rib-eye, top sirloin or tenderloin can all work, but the cooking time will change with the cut and thickness. What matters most is that the steaks are evenly shaped and dry on the surface before they enter the skillet.

The demi-glace must be prepared and ready to use. Do not measure one full cup of concentrated demi-glace paste into the pan. If using a commercial concentrate, dilute it according to the package directions first. The finished liquid should pour like stock when it goes into the skillet and thicken as it reduces.

Cremini or white button mushrooms both work. Slice them evenly so they brown at roughly the same rate. I prefer to cook the mushrooms before adding the shallots because the mushrooms release quite a bit of water at first. This lets the moisture evaporate without overcooking the shallots.

Yukon Gold or another yellow-fleshed potato is a good choice for the Parisian potatoes. They hold together well after simmering and develop a golden surface in the skillet. Starting with a little over 2 pounds of whole potatoes should produce enough potato balls for three servings, with trimmings left over.

Step-by-Step Instructions

Shape and Parboil the Potatoes

Peel and rinse the potatoes. Press a melon baller firmly into the potato, rotate it through the flesh and lift out a rounded ball. Continue around each potato, cutting as many evenly sized balls as possible.

Do not worry if every piece is not perfectly round. Similar size matters more than perfect shape because it controls how evenly they cook.

Bring a pot of salted water to a gentle boil. Add the potato balls and simmer for 5 to 7 minutes. They should be partly cooked but not soft enough to break. Insert the tip of a small knife into one potato. It should enter with some resistance in the centre.

Drain the potatoes and spread them on a plate or tray for 2 to 3 minutes. Letting the steam escape dries the surface and helps the potatoes brown instead of sticking.

Brown the Parisian Potatoes

Heat duck fat or neutral oil in a wide skillet over medium-high heat. Add the drained potatoes in one layer. Let them sit long enough to colour before turning them.

Cook for 10 to 15 minutes, rolling the potatoes occasionally so several sides become golden. Reduce the heat if the pan begins to smoke. The sound should be a steady sizzle, not a violent crackle.

Add the butter when the potatoes are nearly tender. Once the butter foams, add the minced garlic and cook for only 30 to 60 seconds. The mistake to avoid is adding raw garlic at the beginning. It will burn before the potatoes finish cooking.

Add the parsley, season with salt and pepper, then remove the pan from the heat. Keep the potatoes warm while preparing the steaks.

Sear the Steaks

Heat the oven to 425°F if the steaks are more than 1 inch thick. Pat the beef dry, then season both sides with salt and black pepper.

Heat a heavy oven-safe skillet over high heat. Add the duck fat or neutral oil. When the fat shimmers and moves easily across the pan, add the steaks without crowding them. Cook in batches if necessary.

Sear the first side for 2 to 3 minutes without moving the meat. Turn the steaks once a dark brown crust has formed, then sear the second side for about 2 minutes.

For thick steaks, transfer the skillet to the oven and cook until the centre reaches 125 to 130°F for medium-rare. Depending on the cut and thickness, this may take another 3 to 6 minutes. Thinner steaks can finish entirely on the stovetop.

Transfer the steaks to a warm plate and rest them for 5 to 8 minutes. Their internal temperature will continue to rise slightly as they rest.

Build the Cognac Mushroom Sauce

Return the steak skillet to medium-high heat. Add the sliced mushrooms and cook until they release their moisture. At first, the skillet may look wet and crowded. Keep cooking until most of that liquid evaporates and the mushrooms begin to brown around the edges.

Add 1 tablespoon of butter and the chopped shallots. Cook for about 2 minutes, stirring regularly, until the shallots soften and smell sweet.

Remove the skillet from direct heat before pouring in the cognac. Return it to medium heat and let the cognac bubble until reduced by roughly half. There is no need to ignite it. Reducing it in the pan gives the sauce a smoother flavour without requiring a flambé.

Stir in the Dijon mustard, followed by the prepared demi-glace. Scrape the bottom of the skillet with a wooden spoon to loosen the browned bits from the steak.

Let the sauce simmer until it lightly coats the back of a spoon. Draw a finger through the sauce on the spoon. The line should remain visible, but the sauce should still pour easily. If it becomes thick or sticky, add a small splash of water or beef stock.

Finish the Sauce and Plate

Taste the sauce before adding more salt. Prepared demi-glace may already contain enough seasoning.

Remove the skillet from the heat and stir in the cold butter. I prefer to finish the sauce away from direct heat because the butter stays emulsified and gives the sauce a smoother shine.

Return the steaks and any juices from the resting plate to the skillet. Turn them once in the sauce and warm for no more than 30 to 60 seconds. Leaving them in a simmering sauce for several minutes can push a medium-rare steak past the desired doneness.

Place one steak on each plate. Spoon the mushrooms and cognac sauce over the beef, keeping part of the crust visible. Add the garlic-parsley Parisian potatoes and serve immediately.

Chef Notes and Mistakes to Avoid

The first important detail is pan space. Three large steaks need a very wide skillet. If they touch each other, the pan temperature drops and moisture collects around the meat. Cooking in two batches is better than forcing everything into one pan.

The second detail is the demi-glace. A concentrated paste and a prepared demi-glace are not interchangeable. The sauce should begin fairly loose and gradually become glossy as it simmers.

Watch the mushrooms rather than relying only on a timer. They are ready for the shallots when the pan no longer looks watery and the edges of the mushrooms have begun to colour.

Finally, do not return the steaks to the sauce too early. Their resting juices belong in the sauce, but the meat itself only needs a brief warm-up before serving.

For another steak prepared with a contrasting sauce, the tarragon cream sauce version is lighter in colour and more herbal. The pan-seared steak with three-cheese sauce is considerably richer and uses a potato gratin instead of pan-browned potatoes.

Storage and Reheating

Store the steak, sauce and potatoes in separate covered containers when possible. Refrigerate them for up to 3 days.

Warm the sauce gently in a small saucepan, adding a spoonful of water if it has become too firm in the refrigerator. Reheat the potatoes in a skillet so they regain some colour. The steak is best warmed briefly over low heat or served sliced at room temperature. Microwaving the entire plate on high can overcook the beef before the sauce and potatoes become hot.

What to Serve With It

The Parisian potatoes already make this a complete main course, but a green vegetable or sharp salad can balance the richness. Browse these vegetable side dishes for beef and other main courses for simple options that will not compete with the cognac sauce.

For a larger dinner, serve a smaller portion of potatoes and add asparagus, green beans or roasted carrots. The sauce is strong enough to carry a plain vegetable without requiring another heavy garnish.

The same meal also fits naturally into a menu of French bistro recipes to make at home.

Substitutions

Brandy can replace cognac in the same quantity. It will not taste identical, but it provides a similar warm fruit and oak character. For an alcohol-free version, use beef stock and allow it to reduce before adding the demi-glace. The final sauce will be less aromatic but still savoury.

White button mushrooms can replace cremini mushrooms. Finely chopped yellow onion can replace the shallots, although its flavour is slightly stronger and less delicate.

Neutral oil can replace duck fat. Prepared beef gravy can replace demi-glace in a practical home version, but it may already be thickened and heavily salted. Add it gradually and reduce it less.

Small yellow potatoes can be cut into evenly sized pieces when a melon baller is unavailable. They will not have the traditional Parisian shape, but the same simmering and pan-browning method still works.

For a different potato presentation, classic pommes boulangères offer soft layered potatoes cooked with stock, while French pommes duchesse use piped seasoned potato. Classic pommes dauphine are another more elaborate French option.

FAQ

What cut of steak works best with cognac sauce?

Strip loin, rib-eye, tenderloin and top sirloin all work. Choose steaks of similar thickness so they finish cooking at roughly the same time.

Can I make the cognac sauce without flambéing it?

Yes. Let the cognac simmer until reduced by approximately half before adding the mustard and demi-glace. Igniting the cognac is not required for a good sauce.

Can I use concentrated demi-glace?

Yes, but it must be diluted according to the product instructions before measuring. The recipe uses one cup of prepared demi-glace, not one cup of concentrated paste.

Why did my sauce become too salty?

The demi-glace may have been highly seasoned, or the sauce may have reduced too far. Do not season aggressively at the beginning, and add water or unsalted stock if the finished sauce is too concentrated.

How do I know when Parisian potatoes are cooked?

A small knife should slide into the centre without hitting a hard core. The outside should be golden, while the interior should feel tender and creamy rather than crunchy.

Can the potatoes be prepared ahead?

They can be shaped and parboiled several hours ahead. Drain, cool and refrigerate them, then brown them shortly before serving.

Is this the same as Steak Diane?

No. Both recipes may use steak, mushrooms, mustard and cognac, but this version uses a darker demi-glace sauce without cream. Steak Diane is generally softer, creamier and more mustard-forward.

What should I do with the potato trimmings?

Keep them submerged in cold water while working, then use them for soup or mashed potatoes. The potato recipe collection has several ideas for using potatoes in different forms.

Pan-Seared Steak with Cognac Mushroom Sauce and Parisian Potatoes

Chef Dumas

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Prep Time 30

Cooking Time 30

Total Time 1

Category Main Dishes > Beef

Cuisine French

Portions 3

Calories 910 kcal

Ingredients

3 boneless beef steaks 7 to 8 ounces each and 1 to 1¼ inches thick
2¼ pounds Yukon Gold potatoes
2 teaspoons kosher salt divided
1 teaspoon freshly ground black pepper divided
2 tablespoons duck fat or neutral oil divided
3½ tablespoons unsalted butter divided
8 ounces cremini mushrooms evenly sliced
2 medium shallots finely chopped
¼ cup cognac
2 teaspoons Dijon mustard
1 cup prepared demi-glace
2 garlic cloves finely minced
3 tablespoons fresh parsley chopped
¼ cup water or unsalted beef stock as needed

Instructions

Peel the potatoes and use a melon baller to cut as many evenly sized potato balls as possible.
Simmer the potato balls in salted water for 5 to 7 minutes, until partly tender, then drain and steam-dry.
Brown the potatoes in 1 tablespoon duck fat over medium-high heat for 10 to 15 minutes.
Add 1½ tablespoons butter and the garlic, cook for 30 to 60 seconds, then add the parsley and season.
Heat the oven to 425°F for steaks thicker than 1 inch.
Pat the steaks dry and season with salt and pepper.
Heat 1 tablespoon duck fat in a heavy skillet and sear the steaks for 2 to 3 minutes on the first side and about 2 minutes on the second.
Finish thick steaks in the oven until they reach 125 to 130°F for medium-rare, then rest for 5 to 8 minutes.
Cook the mushrooms in the steak skillet until their moisture evaporates and their edges begin to brown.
Add 1 tablespoon butter and the shallots, then cook for about 2 minutes.
Remove the skillet from direct heat, add the cognac and simmer until reduced by half.
Stir in the Dijon mustard and prepared demi-glace.
Simmer until the sauce lightly coats a spoon, adding water or stock if it becomes too thick.
Remove from the heat and stir in 1 tablespoon cold butter.
Return the steaks and resting juices to the sauce for 30 to 60 seconds, then serve with the Parisian potatoes.