- Preheat the oven to 350 degrees. Butter a 9×13 casserole dish.
- Chop squash and onion. Put in a large pot, cover with salted water and cook over medium-high heat for about 15 minutes or until the vegetables are tender.
- Drain well. Mix cooked squash and onion with ¼ cup butter, eggs, corn starch, ½ cup cheddar cheese, ½ cup Parmesan cheese, salt, pepper, and cayenne pepper.
- Place mixture into a buttered casserole dish. Top with remaining cheese and butter and bake for about 35 minutes.