Beef Stroganoff

2 Pounds fillet of beef
1 Tablespoon margarine
1 Tablespoon grated onion
1 Pound sliced mushrooms
1/2 Teaspoon salt
1/4 Teaspoon pepper
1/2 Teaspoon basil
1 1/4 Cup warm whipping cream or sour cream
4 Cups cooked noodles
Cut beef into 1/2 inch slices across the grain. Pound them until thin. Cut into strips about 1 inch wide. Melt margarine in a pan. Sauté onion in margarine. Add beef and sauté quickly about 5 minutes, until browned. Remove and keep warm. Add mushrooms to the pan and sauté. Drain and add the beef, salt, pepper, and basil. Heat through. Stir in cream or sour cream. Serve over noodles. Serves 8.