Step 1

Heat half the oil in a large skillet over medium-high heat. Season 2 steaks with 3/4 teaspoon salt and some pepper. Cook until deep golden brown and an instant-read thermometer inserted into the center reaches 130 degrees, about 4 minutes per side. Transfer to a platter, and tent with foil. Repeat with remaining oil and steaks. Let steaks rest in a 250 degree oven.

Step 2

Reduce heat to medium, and add wine to skillet. Cook until almost completely reduced, about 5 minutes. Add beef stock, and cook until reduced to 1/4 cup, about 2 1/2 minutes. Reduce heat to low, and whisk in butter (1 piece at a time) and mustard. Stir in any juices from the platter, and season with salt and pepper. Spoon sauce over steaks.