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Zucchini & Summer Squash Gratin with Parmesan & Fresh Thyme

Mark Ferri

Servings: six to eight as a side dish, four as a main dish.

For this gratin, use all the interesting green and yellow summer squashes (pattypan, scallop, crookneck, butterstick) you find at the farmers’ market.


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

Nutritional Information

  • Nutritional Sample Size based on eight servings
  • Calories (kcal) : 200
  • Fat Calories (kcal): 120
  • Fat (g): 14
  • Saturated Fat (g): 4
  • Polyunsaturated Fat (g): 1
  • Monounsaturated Fat (g): 8
  • Cholesterol (mg): 10
  • Sodium (mg): 540
  • Carbohydrates (g): 12
  • Fiber (g): 3
  • Protein (g): 9


  • 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 minutes. Reduce the heat to medium-low if they’re browning too quickly. Add the garlic and sauté until soft and fragrant, 1 to 2 minutes 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 minutes. Let cool for at least 15 min. before serving.


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Reviews (28 reviews)

  • linlin123 | 08/05/2020

    This turned soooo good! I didn’t have a shallow gratin pan so I used a 3 Qt glass Pyrex dish and it was fine. I will definitely make it again!! I did have extra squash & zucchini left over that I could just sauté.

  • skc921 | 07/31/2020

    Perfect summer vegetable dish! I've made this many, many times over the years and never get tired of it.

    My boyfriend said it reminded him of Ratatouille from the Disney movie. Obviously no eggplant or pepper, but it does have the same beautiful layered vegetables.

    It takes some time to put together, especially picking the thyme leaves. I will do that part while sitting down watching TV. I've substituted dried thyme, but it is best with the 1/4 cup of fresh thyme.

  • magpiet | 07/21/2020

    This gratin is a lovely presentation of a stellar combination of ingredients. I sometimes use sliced mushrooms with the caramelized onions in the base, sometimes drizzle with truffle oil. This is good hot or room temperature so it can be prepared ahead by hours and will be beautiful and very tasty. The longer cooking time suggested makes the juices syrupy and intense but as one reviewer pointed out, it's ready to eat after about 45 minutes, just not as flavorful as when baked the entire hour plus.

  • butterscotch | 07/17/2020

    I've been making this recipe ever since FC first published it a long time ago. It's good any time of year but especially in summer when beautiful golden zucchini are around and tomatoes are at their peak. I sometimes add sliced mini bell peppers to the onion mixture and use rosemary or oregano instead of thyme. I find the baking time in the recipe to be a little too long. My gratins never need more than 55 minutes. And I agree with other comments that the quantity of vegetables specified will completely fill not one but two two-and-half-quart gratin dishes. If you want a side dish for 6 people, you can halve the recipe. But the gratin is so delicious, and the leftovers are so good, that you might as well make the whole thing.

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