Prepare stuffing mix. Cook broccoli/cauliflower and let cool. Combine eggs, onion, soup, mayonnaise together. Place a layer of vegetables into a 2 quart casserole, then a layer of cheese, and then a small amount of sauce. Repeat layers once more or until all ingredients are used. Top with prepared stuffing mix. Sprinkle butter over top. Bake at 350 for 30 minutes