Southern Squash Casserole

Ingredients

4 pounds yellow squash, trimmed, quartered lengthwise and cut into 1-inch pieces
2 pounds zucchini, trimmed, quartered lengthwise and cut into 1-inch pieces
1 tablespoon extra virgin olive oil
1 1/4 teaspoon teaspoon salt
3/4 teaspoon ground black pepper
4 tablespoons unsalted butter
3 medium onions, chopped
4 ounces extra sharp chedder cheese, shredded
4 ounces Swiss cheese
3/4 cup Parmesan cheese, grated
2 large eggs, lightly beaten
3/4 cup sour cream
1/2 cup panko bread crunbs

Directions

1. Preheat the oven to 425F.
2. Combine the squash, zucchini, oil, 1/2 teaspoon of the salt and 1/4 teaspoon of the pepper in a large bowl; toss well. Divide the squashes evenly between 2 nonstick baking sheets. Roast in the upper and lower thirds of the oven, until tender and lightly browned, 30 minutes, rotating pans front to back and top to bottom halfway through. Remove from the oven and transfer to a bowl.
3. Melt 2 tablespoons of the butter in a large nonstick skillet over medium heat. Add the onions and 1/4 teaspoon of the salt; cook, stirring occasionally, until golden, 27-28 minutes. Transfer the onions to the bowl with the squash and let cool 10 minutes. Stir in the cheddar cheese, Swiss cheese, 1/2 cup of the Parmesan cheese, eggs, sour cream and the remaining 1/2 teaspoon salt and 1/2 teaspoon pepper; gently mix then transfer to a ceramic baking dish.
4. Melt the remaining 2 tablespoons butter in a small nonstick skillet over medium heat. Remove from the heat and stir in the remaining 1/4 cup Parmesan cheese and breadcrumbs; stir to combine. Sprinkle the breadcrumb mixture over the squash. Bake until the casserole is set and the breadcrumbs are lightly toasted, 36-38 minutes. Let cool 10 minutes before serving.