Instructions

1. In a medium-sized sauté pan, heat 2 tablespoons of the olive oil and butter over medium-low heat. Add the leeks and sauté , stirring frequently, until they are caramelized and golden brown, about 40 minutes. Toss leeks with thyme then spread the leeks evenly in the bottom of an oiled, 2- quart shallow oven-safe dish or grain pan, preferably oval. Let cool.
2. Preheat oven to 375°. Lightly sprinkle tomato slices with kosher salt and place in a large colander or shallow plate to drain for 10 minutes; discard the collected juices.
3. In a medium-sized bowl, toss the squash slices with 1 1/2 tablespoons of olive oil and lightly season with kosher salt.
4. 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 bit of cheese. Next, lay a row of squash, 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.
5. Season lightly with freshly ground pepper and sprinkle basil over gratin. Combine remaining cheese with panko and evenly spread over gratin. Drizzle the remaining olive oil over gratin.
6. Bake 50-70 minutes or until crust is golden brown and the vegetables have pulled away from the sides of the pan. (Oven temperatures vary: If your gratin top is well-browned after 40 minutes, cover in foil and let cook longer until vegetables have reduced and released most of their water.) Let cool 15 minutes before serving.