2 lbs. yellow squash, sliced
2 lbs. zucchini, sliced
3/4 cup butter, divided
1 1/2 cups diced onion
2 tsp. minced garlic
1/2 c. sour cream
1/2 c. mayonnaise
2 large eggs
2 cups shredded extra sharp Cheddar cheese
1 c. shredded fontina cheese
1 cup panko ( Japanese bread crumbs)
2 tsp. kosher salt
2 tsp. ground black pepper
2 1/2 c. crushed buttery round crackers
1. Preheat oven to 350º. Spray a 13x9 inch baking dish with cooking spray.
2. In a Dutch oven, bring squash, zucchini, and water to cover to a boil over high heat. Cook until just tender, about 5 minutes. Drain well.
3. In a medium skillet, melt 1/4 cup butter over medium- high heat. Add onion and garlic; cook, stirring frequently until tender, about ten minutes. In a large bowl, whisk together sour cream, mayonnaise and eggs. Stir in squash mixture, onion mixture, all cheese, bread crumbs, salt and pepper.
4. In a microwave- safe bowl, melt remaining 1/2 c. butter on medium heat. Stir in cracker crumbs until well combined, and sprinkle onto casserole. Cover with foil.
5.Bake for 20 minutes Uncover and bake until golden brown, 25 to 30 minutes more. Ket stand for 10 minutes before serving.