In skillet fry bacon & until done. Set aside. Use the drippings from the bacon & saute the minced onion about 3 minutes. Blend in flour, sugar, & (salt, if you choose to use) & pepper. Add milk all at once and cook til thick & bubbly. Remove from heat; stir in sour cream. Add beans. Spread 1/3 of the bean mixture in a 1-quart casserole. Sprinkle 1/2 of the Swiss Cheese over beans; repeat layers ending with beans.
Melted butter in a pan, coat the corn flakes in the melted butter until well mixed. Top the beans with the corn flakes. Bake 400 degrees for 20 minutes.