The sweetness of heirloom tomatoes intensifies when baked in creamy layers of caramelized onions and garlic. Fresh thyme seasoned breadcrumbs and Parmigiano-Reggiano cheese melt together and brown to create a crispy topping. Tastes delectable with some chunks of crusty bread to sop up the luscious juices. —kitchen witch
Generously sprinkle tomatoes with salt and let drain in a colander.
Preheat the oven to 350 degrees F. Grease a shallow baking dish with extra-virgin olive oil.
Heat olive oil in a large skillet over medium heat. Add onion and garlic and cook for about five minutes or until onions are translucent, not brown. Sprinkle with salt, pepper, and 1-1/2 teaspoons thyme.
Combine the tomatoes, honey, and black pepper in a large bowl.
Add half of the onion mixture to the bottom of the baking dish and spread in a even layer. Layer half the tomatoes overlap the tomato slices to fit. Season with freshly ground black pepper and add the rest of the onion mixture, another overlapping layer of tomatoes, and freshly ground black pepper
In a medium bowl, mix together bread crumbs, 2 tablespoons olive oil, 1-1/2 teaspoons thyme, cheese, salt and pepper. Mix until all crumbs are moistened. Sprinkle breadcrumb mixture evenly on top of gratin.
Bake for 35 to 40 minutes until crumbs are golden and tomatoes are bubbly. Serve warm or at room temperature.