For this gratin, use all the interesting green and yellow summer squashes (pattypan, scallop, crookneck, butterstick) you find at the farmers' market. Serves six to eight as a side dish, four as a main dish.
For the onions:
2 Tbs. olive oil
2 medium onions (14 oz. total), thinly sliced
2 cloves garlic, minced
To assemble the gratin:
1-1/4 lb. ripe red tomatoes, cored and cut into 1/4-inch slices
3/4 lb. (about 2 small) zucchini or other green summer squash, cut into 1/4-inch slices on the bias
3/4 lb. (about 2 small) yellow summer squash or golden zucchini, cut into 1/4-inch slices on the bias
3 Tbs. olive oil
1/4 cup fresh thyme leaves
1 tsp. coarse salt
1-1/4 cups freshly grated parmigiano reggiano
Freshly ground black pepper to taste
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 min. Reduce the heat to medium-low if they're browning too quickly. Add the garlic and sauté until soft and fragrant, 1 to 2 min. Spread the onions and garlic evenly in the bottom of an oiled 2-qt. shallow gratin dish (preferably oval). Let cool.
To assemble the gratin -- Heat the oven to 375°F. 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 1-1/2 Tbs. of the olive oil, 2 Tbs. of the thyme, and 1/2 tsp. of the salt. Reserve half of the cheese for the top of the gratin. Sprinkle 1 Tbs. of the thyme over the onions in 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 and the remaining 1/2 tsp. salt. Drizzle the remaining 1-1/2 Tbs. olive oil over all. Combine the reserved cheese with the remaining 1 Tbs. thyme 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 min. Let cool for at least 15 min. before serving.
By Susie Middleton, from Fine Cooking #33, pp. 24-29
photo: Mark Ferri