1. Preheat oven to 350°F (175°C) and grease a 9×13-inch casserole dish.

2. In a large skillet, melt 2 tablespoons of butter over medium heat. Add sliced squash and chopped onion; sauté 7–10 minutes until softened.

3. Drain any excess liquid from the skillet.

4. In a mixing bowl, whisk together eggs, sour cream, shredded cheddar cheese, salt, pepper, and optional seasonings.

5. Fold the sautéed squash and onion into the cheese mixture until evenly combined.

6. Transfer the mixture to the prepared casserole dish and spread evenly.

7. Melt remaining 2 tablespoons of butter and toss with breadcrumbs or crushed crackers. Sprinkle evenly over the top.

8. Bake 30–35 minutes until bubbly and golden. For extra crispness, broil 2–3 minutes, watching closely to avoid burning.

9. Let rest 5 minutes before serving.