4 pounds of yellow squash trimmed, quartered lengthwise and cut into 1-inch pieces
2 pounds of zucchini trimmed, quartered lengthwise and cut into 1-inch pieces
1 tablespoon of extra virgin olive oil
1 1/4 teaspoons of salt
3/4 teaspoon of ground black pepper
4 tablespoons of unsalted butter
3 medium onions chopped
4 ounces of Swiss cheese shredded
3/4 cup of Parmesan cheese grated
2 large of eggs lightly beaten
3/4 cup of sour cream
1/2 cup of panko bread crumbs
- Preheat the oven to 425F.
- 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 Circulon 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.
- 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 an 9 x 13-inch baking dish.
- 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.