Zucchini, Squash, and Corn Casserole

INGREDIENTS

• 1 1/2 pounds yellow squash, cut into 1/4-inch-thick slices
• 1 1/2 pounds zucchini, cut into 1/4-inch-thick slices
• 1/4 cup butter, divided
• 2 cups diced sweet onion
• 2 garlic cloves, minced
• 3 cups fresh corn kernels
• 1 1/2 cups (6 oz.) freshly shredded white Cheddar cheese
• 1/2 cup sour cream
• 1/2 cup mayonnaise
• 2 large eggs, lightly beaten
• 2 teaspoons freshly ground black pepper
• 1 teaspoon table salt
• 1 1/2 cups soft, fresh breadcrumbs, divided
• 1 cup freshly grated Asiago cheese, divided