Classic Steak Diane

INGREDIENTS:

Sauce:
½ cup demi-glace
1 tablespoon Dijon mustard
2 teaspoons Worcestershire sauce
1 teaspoon tomato paste
1 pinch cayenne pepper
Steaks:
2 teaspoons vegetable oil
2 (8 ounce) beef tenderloin steaks, fully trimmed, pounded to 1/2 inch thick
Kosher salt and freshly ground black pepper, to taste
1 tablespoon unsalted butter, cut into small chunks
3 tablespoons shallot, minced
¼ cup Cognac or brandy
¼ cup heavy cream
2 teaspoons sliced fresh chives

DIRECTIONS:

Season steaks generously on both sides with salt. Allow steaks to come to room temperature while you make the sauce.
Stir together demi-glace (see Cook’s Note), mustard, Worcestershire sauce, tomato paste, and cayenne pepper in a bowl.
Heat oil in a skillet over very high heat, swirling carefully to evenly cover surface. When oil reaches a smoking point, transfer steaks to oil; add a few chunks of butter. Sear meat on high heat until brown on each side, 2 to 3 minutes per side; keep them on the rare side. An instant-read thermometer inserted into the center should read 125 degrees F (52 degrees C). Transfer steaks to a warm plate.
Stir shallots into skillet; cook until softened, 2 to 3 minutes. Remove skillet from heat; pour in Cognac. Carefully ignite with a fireplace lighter. When alcohol burns off and flames go out, return skillet to high heat and bring to a boil …