Broccoli Bake

2 pkgs. frozen, chopped broccoli, cooked & drained
1 small onion, chopped
3 eggs, beaten
1 cup mayonnaise                                
1 can cream of mushroom soup
1/4 cup cheddar cheese, grated
2 Tblsp. butter
12 Ritz crackers          

Mix broccoli, mayonnaise, cream of mushroom soup, eggs and onion together and put into a 2-quart casserole.  Sprinkle cheddar cheese over mixture to cover.  Crumble the crackers to bread crumb consistency and brown in butter.  Sprinkle crumbs over the top.  Bake at 350 degrees for 30 to 40 minutes.