Heat oven to 350 degrees F. Cook and stir onion in butter until the onions are tender; spread in ungreased 1/2 pan. Top with egg slices; sprinkle with cheese. Beat remaining ingredients except bread. Pour soup mixture over cheese; overlap bread slices buttered side up on top of casserole.

 

Bake uncovered 30-35 minutes or until heated through. Set oven control to broil and broil 1 minute or until bread is toasted.