1. Melt 1 tablespoon butter in a skillet over medium-high heat. Put steaks in skillet and cook until browned on both sides and done to your liking (it's about 8 minutes for rare).
2. Combine lemon juice, mustard and 3 tablespoons softened butter in a little bowl.
3. Put the steaks on plates when they are finished, season with salt & pepper then top with the mustard sauce.