Give this gratin time to cook slowly, releasing juices and then caramelizing slightly. This gentle treatment emboldens flavors and intensifies the sugars. What you’ll get is not just an explosion of summer flavors, bur also a rich, satisfying dish that could easily be the centerpiece of a vegetarian meal. Using the basic recipe, experiment with different vegetable combinations, such as potatoes and eggplant, and also with different cheeses. You’re sure to agree that this dish captures the essence of late summer. Adapted from Fine Cooking.
For the base:
2 Tbs. olive oil
2 medium onions thinly sliced or chunked
2 cloves garlic, minced
2 T fresh herbs such as thyme, oregano, rosemary, basil, parsley (can substitute dried)
To assemble the gratin:
3-4 ripe red tomatoes, cored and cut into 1/4-inch slices to yield 4 C
2-4 zucchinis, yellow squash, or other summer squash, sliced into 1/4 inch rounds to yield 4 C
3-4 T olive oil
1/4 cup fresh thyme leaves, or combination thyme, oregano, rosemary, basil
1 tsp. coarse salt
1-1/4 cups freshly grated cheese, such as Monterey Jack, Gruyere, Parmesan, or a combination
Freshly ground black pepper to taste
2 C Panko bread crumbs
To cook the onions: In a medium skillet, heat the olive oil over medium heat. Add the onions and sauté, stirring frequently, until limp and golden brown, about 20 minutes. Reduce the heat to medium-low if they’re browning too quickly. Add the garlic and herbs, sauté until soft and fragrant, 1 to 2 minutes Spread the onions and garlic evenly in the bottom of a shallow gratin dish (preferably oval). Let cool.
To assemble the gratin: Heat the oven to 375̊F. Put the tomato slices on a shallow plate to drain for a few minutes and then discard the collected juices. In a medium bowl, toss the zucchini and squash slices with 1½ T of the olive oil, 2 T of the thyme, and ½ t salt. Reserve half of the cheese for the top of the gratin. Starting at one end of the baking dish, lay a row of slightly overlapping tomato slices across the width of the dish and sprinkle with a little of the cheese. Next, lay a row of zucchini, overlapping the tomatoes by two-thirds, and sprinkle with cheese. Repeat with a row of squash, and then repeat rows, sprinkling each with cheese, until the gratin is full.
Season lightly with pepper; drizzle with olive oil over all. In a small bowl, combine Panko breadcrumbs, 1 T thyme, 1 T olive oil and sprinkle this over the whole gratin. Cook until well-browned all over and the juices have bubbled for a while and reduced considerably, 65 to 70 minutes. Let cool for at least 15 min. before serving.