Tomato Gratin | America's Test Kitchen

Ingredients

• 3 pounds plum tomatoes , cored and sliced into 1/4-inch-thick rings
• Salt and pepper
• 1/2 teaspoon sugar
• 1 cup panko bread crumbs
• 2 ounces Parmesan cheese , grated (1 cup)
• 1/4 cup extra-virgin olive oil
• 1 pound onions , halved and sliced thin
• 1 tablespoon chopped fresh thyme
• 2 garlic cloves , minced