Marinate steak for 24 hours; wipe dry.

SAUCE:

4 sliced onions
3 tbsp. butter
1 c. water
Salt & pepper to taste
1 clove garlic, crushed
3 tbsp. chives
1 tsp. prepared mustard
2 tbsp. tomato paste
1 dash of Worcestershire sauce

Saute onions in water and butter. Season with salt and pepper. Add remaining ingredients and simmer a few minutes. Broil steak to desired doneness. Put on platter and pour sauce over steak. Add buttered sauteed mushrooms.