1 1/2 to 2 pounds top sirloin roast, trimmed 
1 teaspoon salt 
1 teaspoon ground black pepper 
2 tablespoons butter or margarine 
1 tablespoon olive oil 
1 tablespoon all-purpose flour 
1 cup beef bouillon or broth 
1 medium onion, quartered and sliced 
3 tablespoons sour cream, room temperature 

Cut beef into narrow 2-inch long strips about 1/2-inch thick. Sprinkle meat with salt and pepper. Melt 1 tablespoon butter in a medium saucepan. Blend in flour; gradually stir in beef broth, stirring and cooking until thickened and smooth. Heat remaining 1 tablespoon of butter and 1 tablespoon olive oil in a small saucepan over medium heat; quickly brown meat strips and onion on all sides. Add meat and onions to beef sauce. Cover and cook on low for 10 minutes; stir in sour cream and heat through but do not boil. Serve over buttered noodles or rice.
Serves 4.