Pat steak dry with paper towels and season with salt. Allow steaks to rest at room temperature for 15 to 20 minutes.
Melt 1 tablespoon of butter in a large skillet over medium-high heat.
Add the meat and cook for 2 minutes on the first side. Turn and cook for about 30 seconds on the second side. Add shallots and cook for approximately 30 seconds.
Remove steak and place on a plate. Cover the steaks with another plate so they stay warm. Add sliced mushrooms and cook until they are soft. Tilt the pan towards you and add the Marsala.
Tip the pan away from yourself and ignite the Marsala with a match. (Alternatively, remove the pan from the heat to ignite, and then return to the heat.) When the flame has burned out, add the mustard, cream, butter, and Worcestershire sauce. Serve sauce over steaks. Garnish with minced parsley leaves.