Paula Deen's Cheesy Squash Casserole

This is another one we had at Lady & Sons on Mother's Day-we've had it twice and it SURE is delicious! This makes a LOT-a lot more than the three of us can eat at one sitting so feel free to back off on the squash use if you need or want to.

1 tablespoon vegetable oil
6 medium yellow summer squash, thinly sliced
1 large Vidalia onion, thinly sliced
1 tablespoon butter
1/2 cup grated Parmesan
1 cup shredded sharp Cheddar
1/2 cup sour cream
Salt and freshly ground black pepper
1 sleeve crackers, crushed medium to fine (recommended: Ritz, or I sprinkle mine with French's French Fried Onions)

Preheat the oven to 350 degrees. Grease a 2-quart casserole dish. Heat the oil in a large skillet over medium heat. Saute the squash, onion, and butter until soft. Transfer to a bowl and stir in the Parmesan, Cheddar, and sour cream. Add salt and pepper, to taste. Place in the prepared casserole dish and sprinkle the cracker crumbs evenly over the top. Bake for 20 minutes or until the top is golden and bubbly.