Mustard is not just for hot dogs anymore. This steak is fast and easy to prepare and would go well with most any side dish. Once the mustard has been added, do not allow to boil or the sauce will become unpleasant.
Season steaks on both sides with salt and pepper. Heat oil in a large heavy skillet over high heat until almost smoking. Add steaks and cook 4 to 5 minutes and turn. Continue cooking another 4 or 5 minutes.until desired doneness. Remove steaks to a platter and keep warm.
Pour off fat from skillet. Add butter, then shallots. Add cognac and carefully ignite it. Add cream and bring to a boil, cook while stirring about 5 minutes. Remove from heat and stir in the mustard. Add salt and pepper to taste. Serve over steaks.