My husband made this for me today and it was delicious.
1/2 lb. mushrooms
1 lg. onion
3/4 slices 4 beef tenderloin steaks (filet mignon)
1/2 c. water
2 tbsp. prepared mustard
4 tbsp. capers, drained
In 2 tablespoons butter cook onion until tender. Remove to bowl.
In same pan with drippings, cook mushrooms and steak over medium-high heat until desired doneness, about 6 minutes for rare. Into remaining drippings, stir water, mustard, and capers over medium heat; cook, stirring until mixture thickens and onions. Pour over and around steaks.