Tomato Gratin

1. 1

   Preheat the oven to 425.

2. 2

   Oil an 8-by-12-inch baking dish.

3. 3

   In a medium skillet, heat the olive oil.

4. 4

   Add the onion and thyme and cook over moderate heat, stirring occasionally, until the onion is softened, about 7 minutes.

5. 5

   Scrape the onion into the prepared baking dish and spread evenly over the bottom.

6. 6

   Arrange the tomato slices over the onion in overlapping rows.

7. 7

   Season with salt and pepper and drizzle with the balsamic vinegar.

8. 8

   Dot the tomatoes with the butter and sprinkle the Parmigiano-Reggiano on top.

9. 9

   Bake on the upper rack for about 15 minutes, until the cheese starts to brown and the gratin is bubbling.

10. 10

    Let rest for about 5 minutes before serving.

* Per serving · 4 servings · Values may vary.