Salt and pepper the steaks. Heat a tablespoon of butter in a skillet over medium-high heat and pan-broil the steaks in it, about two minutes per side for medium rare. Remove and keep warm.
Lower the heat and add the Worcestershire, mustard, and Scotch to the skillet. Stir the bottom to release the little pieces of beef crust. If you know what you're doing, you can flame it. However, I recommend that you just bring it to a light boil and reduce it down to just about two tablespoons of liquid.
Add the shallots and tarragon. Saute until the shallots are tender.
Add demi-glace, cream, mushrooms, and peppercorns. Bring to a boil and reduce until appropriately thick. Nap the sauce over the steaks and serve immediately.