Beef Stroganoff - cooking recipe

Ingredients

2 lb. lean sirloin steak (1/2 x 2-inch thick slices)
2 tsp. salt
1/2 tsp. fresh ground pepper
4 Tbsp. butter
1 medium onion, thinly sliced
1 Tbsp. flour
1 tsp. mustard powder or 1 Tbsp. Dijon-type, prepared
1/2 c. dry white wine
2 tsp. tomato paste
1 Tbsp. minced onion
1/2 lb. mushrooms, thinly sliced
2 Tbsp. dry white wine
1 c. sour cream, preferably warm

Preparation

Pound meat between sheets of wax paper with a mallet. Sprinkle with salt and pepper and let stand 15 minutes.
Heat 2 tablespoons butter in deep frypan.
Add onion and cook over medium heat; stir constantly for about 5 minutes or until softened.
Stir in flour and mustard and cook for 1 minute, stirring constantly. Reduce heat to low, cover pan and simmer for 5 to 10 minutes, stirring frequently.