Meanwhile, in 3-quart saucepan, melt 1/4 cup of the butter over medium-high heat. Cook onion in butter 4 minutes, stirring occasionally, until tender. Reduce heat to medium. Sprinkle onion with flour; cook 3 minutes longer, stirring constantly. Stir in broth. Heat to boiling. Remove from heat. Stir in black pepper, salt, red pepper and sour cream with wire whisk until blended. Stir in green beans. Spoon mixture into baking dish.