Peel cushaw; scoop out seeds; cut up and boil until tender. Use 2 cups while still hot (rest may be frozen). Add 1/2 stick butter, salt and pepper. Stir until mashed. Beat 1 egg; chop 1 onion; crumble 2 slices bread. Add 3/4 cup sour cream, 1/2 cup Cheddar cheese, 1/2 cup Velveeta (cut up small). Add squash. Stir; cook in casserole dish 30 minutes at 350 degrees.