Chef John's Classic Steak Diane

Prepare the steaks by sprinkling them liberally on both sides with salt. Meanwhile, bring the steaks to a comfortable temperature while you prepare the sauce.

Combine demi-glace in a bowl with mustard, Worcestershire sauce, tomato paste, and cayenne pepper. Mix well to create a harmonious blend.

Heat oil in a skillet over extremely high heat, taking care to coat the surface evenly. When the oil reaches its boiling point and starts smoking, carefully place the steaks into the hot oil; add a few pieces of butter to enhance flavor. Sear the meat on high heat until it develops a rich brown color on both sides, taking about 2 to 3 minutes per side; aim for a rare finish. Use an instant-read thermometer to check the internal temperature, aiming for 125 degrees F (52 degrees C). Transfer the steaks to a warm plate.

Add shallots to the skillet and cook until they become soft and fragrant, taking about 2 to 3 minutes. Remove the skillet from heat; carefully pour in Cognac and ignite it using a fireplace lighter. Wait until the alcohol burns off and the flames die down, then return the skillet to high heat and bring it to a rolling boil; cook, stirring constantly, until the sauce reduces slightly. Add the demi-glace mixture, cream, and any juices that have accumulated from the steak during cooking. Cook on high heat just until the sauce thickens, taking about 3 to 5 minutes. Transfer the steaks back to the pan and reduce heat to a low simmer. Gently cook until the meat is heated through and cooked to your desired level of doneness.

Transfer the steaks to hot plates and serve with a generous helping or two of sauce. Sprinkle with chives to complete the dish.