1. Preheat broiler.
2. Saute onions in 3 tablespoons butter until onions are translucent.
3. Add flour, salt, pepper, broth and sherry and cook, over medium heat, stirring constantly, until thickened.
4. Pour into broiler proof casserole dish.
5. In a small bowl, combine croutons with melted butter then evenly spread onto mixture in casserole dish.
6. Sprinkle with cheese and place under broiler until cheese is melted, about 1-2 minutes.
Be sure to use nice sweet onions for this casserole dish. The beef broth and sherry give the dish all the bite and tangy flavor it needs. The Swiss cheese adds that nice smooth, creamy flavor. You can substitute provolone cheese for a smoky flavor if you'd like.
If you use the sweetest onions you can get and lots of cheese, even the kids will eat this!