Summer Gratin

This is so good! It's definitely not a dish you can throw together at the last minute (it has to bake for over an hour!), but it was well worth the effort. It has cheese - I'm sorry! I can't get off the cheese! :)

2 Tablespoons olive oil
2 medium onions (about 14 ounces total), thinly sliced
1 clove garlic, minced
1 1/4 pounds small ripe tomatoes, cored & cut into 1/4-inch slices
3/4 pound (about 2 small) zucchini, cut into 1/4-inch slices
3/4 pound (about 2 small) yellow summer squash, cut into 1/4-inch slices
3 Tablespoons olive oil, divided
1/4 cup chopped fresh thyme leaves, divided (I used dried)
1 teaspoon salt, divided
1 1/4 cups freshly grated Parmesan cheese, divided in half
freshly ground black pepper to taste

Directions:
1. In a medium skillet, heat the 2 Tablespoons olive oil over medium heat. Add the onions and sauté, stirring frequently, until limp and golden brown (about 20 minutes). Reduce heat to medium-low if they're browning too quickly. Add garlic in the last minute or two.

2. Spread onions evenly in the bottom of an oiled 2-quart shallow dish. Let cool.

3. Preheat oven to 375°F.

4. Put tomato slices on a shallow plate to drain for a few minutes, and then discard the collected juices.

5. In a medium bowl, toss zucchini and squash slices with 1 1/2 Tablespoons olive oil, 2 Tablespoons thyme, and 1/2 teaspoon salt.

6. Sprinkle 1 Tablespoon thyme over the onions in the dish. 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, then repeat rows, sprinkling each with cheese, until the dish is full. You may want to press the rows tight (like you're trying to stand them more upright) two or three times as you go along. Season lightly with pepper and remaining 1/2 teaspoon salt. Drizzle remaining 1 1/2 teaspoons olive oil over everything.

7. Combine remaining cheese with remaining 1 Tablespoon thyme and sprinkle this liberally over the whole gratin. Bake 65-70 minutes, until well-browned all over and juices have bubbled for a while and reduced considerably. Let cool at least 15 minutes before serving.

Source: RecipeGirl.com (via Fine Cooking)