French Onion Soup Casserole

8 medium onions, sliced
5 T butter, divided
1/4 C sherry or additional beef broth
1 1/2 C salad croutons
1/2 C shredded swiss cheese
3 T grated parmesan
2 T all purpose flour
Dash of pepper
3/4 C beef broth

In large skillet, saute onions in 3 T butter until tender
Stir in flour and pepper until blended-gradually add sherry(or the addtional broth) and broth
Bring to a boil-cook and stir for 3 minutes or until thickened
Tranfer to an UNGREASED 9" baking pan
Melt remaining butter,add to croutons-toss to coat
Spoon croutons over onion mixture
Sprinkle with cheeses
Broil 1-2 minutes or until cheese is melted