1. Melt butter in saucepan over low heat; stir in flour, salt, pepper, sugar and onions. Add sour cream, stirring until smooth. Increase heat to medium and cook until bubbly and thickened, stirring constantly. Fold in green beans. Pour into greased 1 1/2-quart baking dish.
2. Toss together Special K and grated cheese. Sprinkle over beans.
3. Bake in moderate oven (350° F.) about 20 minutes or until bubbly.