Cook cabbage in small amount of boiling water until tender, drain very well. Set aside.
In a large skillet, saute' onions in the 5 Tbsp. butter until tender. Add soup to onions in skillet and mix well. Add cheese; stir over low heat until cheese melts. Remove from heat. Stir in drained cabbage, salt and pepper. Turn into a buttered 2 quart baking dish.
Melt the 1 Tbsp. butter in microwave and mix with bread crumbs; sprinkle over top of casserole.
Bake uncovered at 350 degrees for 30 minutes.