Ingredients

Filling:

3 pounds yellow squash, cut 1/8-inch thick

2 pounds zucchini, cut 1/8-inch thick

3 tablespoons unsalted butter, plus additional for greasing

1 medium yellow onion, minced

1 medium clove garlic, minced

2 large eggs, lightly beaten

8 ounces sour cream

1/3 cup mayonnaise

4 ounces sharp white Cheddar, freshly grated

1 teaspoon chopped fresh thyme

10 fresh basil leaves, chiffonade

2 teaspoons kosher salt

1/4 teaspoon freshly ground black pepper

3 tablespoons minced fresh flat leaf parsley

Topping:

32 butter crackers, crushed

2 tablespoons unsalted butter, melted

3 tablespoons grated Parmesan

Directions

1. For the filling: Heat a large high-sided skillet over medium-high heat. Add half the squash and zucchini and a pat of butter if desired. Stir, then reduce the heat to medium. Cover and let steam (you are not looking to get color on the squash, just to release its moisture), stirring occasionally, about 5 minutes. Transfer to a colander and let drain for at least 1 hour. Repeat with the second half of the squash and another pat of butter.
2. When ready to bake, preheat the oven to 350 degrees F and grease a 9-by-13-inch casserole dish with butter.
3. In the same skillet, heat the remaining tablespoon butter and cook the onions until translucent, about 5 minutes. Stir in the garlic and cook for an additional minute. Allow to cool slightly.
4. In a large bowl, combine the eggs, sour cream, mayonnaise, Cheddar, thyme, basil, salt, pepper and 2 tablespoons parsley. Stir in the squash mixture and the onion mixture. Transfer to the prepared baking dish.
5. For the topping: In a small bowl, mix the cracker crumbs with the melted butter. Sprinkle over the top of the casserole. Sprinkle over the Parmesan and bake until golden brown, about 30 minutes. Garnish with the remaining tablespoon parsley. Allow the casserole to rest for 10 to 15 minutes before serving.