Melt butter in shallow pan, add steaks, cook until done as desired. Remove meat from pan, add peeled whole onions, cook few minutes, remove from pan. Stir in flour, cook 1 minute. Gradually stir in water and wine, add brandy, crumbled stock cube, tomato paste and mustard, mix well.

Place steaks in small oven-proof dish, add onions and mushrooms, pour prepared sauce over, cover, bake in moderate oven 15 to 20 minutes.