Summer Squash Gratin | America's Test Kitchen

Ingredients

• 2 tablespoons unsalted butter , softened, plus 4 tablespoons melted
• 2 onions , halved and sliced thin
• Salt and pepper
• 3 garlic cloves , minced
• 1 tablespoon minced fresh thyme
• 1/2 cup dry white wine
• 1/2 cup pitted kalamata olives , chopped fine
• 1/4 cup chopped fresh basil
• 1 1/2 pounds zucchini , sliced 1/4 inch thick
• 1 1/2 pounds yellow summer squash , sliced 1/4 inch thick
• 1 cup panko bread crumbs
• 2 ounces Parmesan cheese , grated (1 cup)