Steak Diane Recipe

Temper and season steaks

Remove filet medallions from the refrigerator 30–45 minutes before cooking so they come to near room temperature. Pat dry with paper towels. Season both sides evenly with kosher salt and freshly ground black pepper.

Sear fillets

Heat a large heavy skillet (cast-iron preferred) over medium-high heat until very hot. Add 1 tablespoon olive oil and 1 tablespoon unsalted butter. When butter foams and oil shimmers, add the medallions (do not overcrowd; cook in two batches if needed). Sear without moving for 2–3 minutes to form a brown crust, flip and sear the other side 2–3 minutes for medium-rare (adjust time for desired doneness). Remove steaks to a warm plate and tent loosely with foil to rest 8–10 minutes. Reserve pan drippings for the sauce.

Cook mushrooms

In the same skillet over medium heat, add 1 tablespoon butter. Add the sliced mushrooms in a single layer and allow them to brown without stirring for 2 minutes, then stir and cook another 3–4 minutes until golden and any liquid has evaporated.

Aromatics

Add the minced shallots and garlic to the mushrooms and cook 1–2 minutes until fragrant and softened, taking care not to burn the garlic.

Flambé (optional) and deglaze

Carefully add the brandy or cognac to the pan. If comfortable and safe, tilt the pan slightly and ignite with a long match to flambé until flames subside (about 5–10 seconds). If not flambéing, allow the alcohol to simmer and reduce for 1 minute to burn off the raw spirit. Scrape up any browned bits from the pan with a wooden spoon.

Build the Diane sauce

Stir in the Dijon mustard and Worcestershire sauce, then add the beef demi-glace. Bring to a gentle simmer and reduce for 2–3 minutes until slightly thickened. Whisk in the remaining 1 tablespoon butter and the heavy cream to finish the sauce, stirring until glossy. Taste and season with 1/2 teaspoon salt and 1/2 teaspoon black pepper. Stir in the chopped parsley and thyme leaves.

Finish steaks

Return the rested medallions to the skillet, spoon the sauce and mushrooms over them, and warm through for 1 minute (do not overcook). Remove from heat and keep warm until plating.

Cook potatoes

Place the cut potatoes in a large pot and cover with cold water by 1 inch. Add 1 teaspoon salt. Bring to a boil over high heat, then reduce to a simmer and cook until potatoes are fork-tender, about 12–15 minutes.

Drain and dry

Drain potatoes well and return them to the hot pot. Over low heat, gently shake the pot for 30–60 seconds to evaporate excess moisture.

Whip

Warm the milk, cream and 3 tablespoons butter together until butter melts. Using a potato ricer, masher, or electric hand mixer on low, mash the potatoes while gradually adding the warmed milk mixture until smooth and fluffy. Season with 1 teaspoon salt and 1/4 teaspoon pepper. Taste and adjust seasoning. Keep warm until serving.

Prepare and cook

Preheat oven to 425°F (220°C) or use a hot skillet. If roasting: place trimmed asparagus on a baking sheet, toss with 1 tablespoon olive oil, 1/2 teaspoon salt, and 1/4 teaspoon pepper. Roast for 8–10 minutes until tender-crisp and slightly charred. If pan-searing: heat a skillet over medium-high heat, add oil, then asparagus and cook, turning occasionally, 6–8 minutes until tender-crisp.

Finish

Remove from heat and, if using, sprinkle with lemon zest for brightness. Keep warm for plating.