Beef Stroganoff

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