Italian-ish Squash Casserole

3 tablespoons extra virgin olive oil

2 tablespoons butter

8 heaping cups chopped yellow squash

1 large onion, chopped

1 cup shredded Parmesan cheese

1/2 cup mayonnaise

Kosher salt and coarsely ground black pepper to taste

1 cup Italian style panko bread crumbs

3 tablespoons melted butter

Preheat the oven to 350 degrees. Spray 9 x 9 inch casserole dish with nonstick cooking spray.

Heat the oil and 2 tablespoons butter in a large skillet over medium heat. Add the squash and onion, and cook until squash is crisp-tender. Transfer to a large bowl and stir in the Parmesan and mayonnaise. Add salt and pepper to taste.  Pour into casserole dish.  Stir together the panko crumbs and 3 tablespoons melted butter and sprinkle on the squash.  Bake for 20 minutes or until the top is golden brown and bubbly.