Store bought demiglace, which is a concentrated stock is the base for this rich, smooth sauce. Serve it with some seasonal vegetables or a sweet potato mash.
Liberally salt and pepper the room temperature steaks. I like to let them sit for at least an hour with the salt on, in order to draw out the poisture for a nice sear.
In a cast iron pan, sear the steak in the butter over high heat until medium rare (130 degrees internally) or 3-4 minutes per side. Set aside.
In the same pan, saute the shallots in the pan used for cooking the steaks, stir in the mustard, Worcestershire and demiglace. Add Madeira, lemon and parsley.
Remove from heat. Add butter. Season with salt and pepper, and pour over steaks.