Classic Zucchini Casserole

Name: Classic Zucchini Casserole
Ingredients: 3 tablespoons unsalted butter, divided; 3 pounds medium zucchini, sliced (about 6 zucchini); 2 cups sliced sweet onion; 2 large eggs, lightly beaten; ½ cup plain whole-milk Greek yogurt; ¼ cup canola mayonnaise; 2 teaspoons chopped fresh thyme; ¾ teaspoon ground pepper; ½ teaspoon salt; ¾ cup shredded Cheddar cheese; 15 round buttery crackers (such as Ritz), coarsely crushed (about 2/3 cup)