Creating Old-School Squash Casserole is a straightforward process. Just follow these steps to ensure the perfect outcome:

1. Preheat Oven: Preheat your oven to 350°F (175°C).
2. Prepare Squash: In a large pot, bring water to a boil. Add the sliced squash and chopped onion, cooking until tender (about 5 minutes). Drain and set aside.
3. Mix Ingredients: In a large mixing bowl, combine the cream of mushroom soup, sour cream, salt, pepper, and garlic powder. Stir until smooth.
4. Combine Squash: Add the drained squash and onion to the mixture. Fold gently until the squash is well coated.
5. Add Cheese: Stir in half of the cheddar cheese until thoroughly mixed.
6. Layer in Dish: Transfer the mixture to a greased casserole dish. Smooth out evenly.
7. Top with Crackers: In a separate bowl, combine crushed butter crackers, melted butter, and the remaining cheddar cheese. Mix until evenly coated, then sprinkle over the top of the casserole.
8. Add Parmesan: Sprinkle the grated Parmesan cheese evenly over the cracker topping for added flavor.
9. Bake: Place in the preheated oven and bake for 30-35 minutes or until the top is golden brown and bubbly.
10. Cool and Serve: Remove from the oven and allow to cool for a few minutes before serving.