Pat the steaks dry with paper towels and season with salt. Allow them 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 steaks and cook for 2 minutes on the first side. Turn and cook for about 30 seconds on the second side.
Add the shallots and cook for approximately 30 seconds.
Remove the steaks from the pan and place them on a plate. Cover the steaks with another plate so they stay warm.
Add the sliced mushrooms to the skillet and cook until soft.
Tilt the skillet toward you and add the Marsala. Tilt the pan away from you 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, Worcestershire sauce, and the remaining butter. Stir to combine.
Serve the sauce over the steaks and garnish with minced parsley leaves.