A cheesy casserole to feed a crowd, this riff on classic mac and cheese incorporates spinach for some color and a topping made from crushed crackers for crunch.
1. Preheat oven to 400°F. Lightly grease a 3-qt baking dish and place on a baking sheet. Cook the cavatappi according to package directions, draining about 3 min. before al dente.
2. Meanwhile, squeeze the spinach until very dry. In a food processor, pulse the crackers until finely crushed and transfer to medium bowl. Stir in the Parmesan and butter. Set aside.
3. In a 6- to 7-qt pot, whisk the cornstarch and ½ cup milk until smooth. Gradually whisk in the garlic powder and remaining 4 cups milk. Heat to a boil on medium-high, whisking constantly. Reduce heat to medium-low.
4. To pot, add the American and Cheddar cheeses one handful at a time, stirring until smooth after each addition. Season with salt and pepper to taste. Stir in the spinach and par-cooked pasta until well combined.
5. Transfer mixture to baking dish and top with reserved cracker crumbs. Bake 15–20 min., until top is golden brown.