1-Melt 1 tablespoon of butter in a large pan over medium heat. Add the diced onion and sauté for 7 to 8 minutes until it’s soft and translucent. This builds a flavorful base for the casserole.

2-Add the sliced yellow squash to the pan and cook for 10 to 12 minutes until it’s soft, stirring often to release moisture and prevent browning. Don’t skip this step, as it helps avoid a watery result.

3-Drain the cooked squash and onions in a towel-lined colander for at least 5 minutes, pressing out extra moisture. This is crucial for a firm casserole.

4-In a bowl, mix the drained squash and onions with garlic powder, salt, pepper, sour cream, beaten egg, shredded cheddar cheese, and ¼ cup grated Parmesan cheese. Stir until everything combines smoothly.

5-Melt the remaining 3 tablespoons of butter and mix it with the crushed butter crackers and the remaining ¼ cup Parmesan cheese. This creates the crispy topping that everyone loves.

6-Transfer the squash mixture into a 1.5-quart baking dish, like an 8×8 inch pan. Spread it out evenly for consistent baking.

7-Sprinkle the butter and cracker topping over the casserole. Bake at 350 degrees Fahrenheit for 25 minutes until it’s golden brown and bubbly.