Season both sides of beef with salt and pepper. Melt butter in a heavy skillet; add mustard and shallots. Saute over medium heat 1 minute. Add steaks and cook approximately 4 minutes on each side for medium-rare. Remove steaks to serving plate and keep warm. Flame pan with cognac and reduce heat. Add into pan 1 Tbsp. butter, sherry, Worcestershire sauce and chives. Cook for 2 minutes. our sauce over steaks and sprinkle with parsley.