Ingredients

Instructions

  1. To cook the onions: In a medium skillet, heat the olive oil over medium heat.
  2. Add the onions and sauté, stirring frequently, until limp and golden brown, about 20 minute Reduce the heat to medium-low if they're browning too quickly.
  3. Add the garlic and sauté until soft and fragrant, 1 to 2 minutes.
  4. Spread the onions and garlic evenly in the bottom of an oiled 2-quart shallow gratin dish (preferably oval).
  5. Let cool.
  6. To assemble the gratin: Heat the oven to 375°F.
  7. Put the tomato slices on a shallow plate to drain for a few minutes and then discard the collected juices.
  8. In a medium bowl, toss the zucchini and squash slices with 1-1/2 Tbsp of the olive oil, 2 Tbsp of the thyme, and 1/2 teaspoons of the salt.
  9. Reserve half of the cheese for the top of the gratin.
  10. Sprinkle 1 Tbsp of the thyme over the onions in the gratin.
  11. 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.
  12. Next, lay a row of zucchini, overlapping the tomatoes by two-thirds, and sprinkle with cheese.
  13. Repeat with a row of squash, and then repeat rows, sprinkling each with cheese, until the gratin is full.
  14. Season lightly with pepper and the remaining 1/2 tsp salt.
  15. Drizzle the remaining 1-1/2 Tbsp olive oil over all.
  16. Combine the reserved cheese with the remaining 1 Tbsp thyme and sprinkle this over the whole gratin.
  17. Cook until well-browned all over and the juices have bubbled for a while and reduced considerably, 65 to 70 minutes.
  18. Let cool for at least 15 minutes before serving.