Summer Vegetable Gratin

May 26, 2017

6-8 servings as a side dish or 4 as a light entree


  • 6 tbsp extra virgin olive oil
  • 1 lb zucchini, ends trimmed and sliced crosswise into 1/4 inch thick slices
  • 1 lb yellow summer squash, ends trimmed and sliced crosswise into 1/4 thick slices **
  • 2 tsp table salt
  • 1 1/2 lb ripe tomatoes (3 to 4 large), sliced 1/4 inch thick
  • 2 medium onions, halved lengthwise and sliced thin pole to pole (about 3 cups)
  • 3/4 tsp ground black pepper
  • 2 medium garlic cloves, minced or pressed through a garlic press
  • 1 tbsp minced fresh thyme leaves
  • 1 large slice white sandwich bread, torn into quarters
  • about 1 cup parmesan cheese
  • 2 medium shallots, minced (about 1/4 cup)
  • 1/4 cup chopped fresh basil leaves

**The success of this recipe depends on good-quality of produce. Zucchini and summer squash should be of roughly the same diameter. While the visual contrast of zucchini and summer squash is nice, you can use just one or the other. A similarly-sized broiler-safe gratin dish can be substituted for the 13 by 9-inch baking dish. Serve the gratin alongside grilled fish or meat and accompanied by bread to soak up any flavorful juices.


  1. Adjust oven rack to upper-middle position and heat oven to 400 degrees. Brush 13 x 9-inch baking dish with 1 tbsp oil. Set aside
  2. Toss zucchini and summer squash slices with 1 tsp salt in large bowl; transfer to a colander set over a bowl. Let stand until zucchini and squash release at least 3 tbsp of liquid, about 45 minutes. Arrange slices on triple layer paper towels; cover with another triple layer of paper towels. Firmly press each slice to remove as much liquid as possible.
  3. Place tomato slices in single layer on double paper towels and sprinkle evenly with 1/2 tsp salt, let stand 30 minutes. Place second double layer paper towels on top of tomatoes and press firmly to dry tomatoes.
  4. Meanwhile, heat 1 tbsp oil in a 12-inch nonstick skillet over medium heat until shimmering. Add onions, remaining tsp salt and 1/4 tsp pepper; cook, stirring occasionally until onions are softened and dark golden brown, 20 to 25 minutes. Set onions aside
  5. Combine garlic, 3 tbsp oil, remaining 1/2 tsp pepper and thyme in small bowl. In a large bowl, toss zucchini and summer squash in half of oil mixture, then arrange in greased baking dish. Arrange caramelized onions in an even layer over squash. Slightly overlap tomato slices ni single layer on top of onions. Spoon remaining garlic-oil mixture evenly over tomatoes. Bake until vegetables are tender and tomatoes are starting to brown on edges, 40 to 45 minutes.
  6. Meanwhile, process bread in food processor until finely ground, about 10 seconds (You should have about 1 cup crumbs). Combine bread crumbs, remaining tablespoon oil, parmesan and shallots in medium bowl. Remove baking dish from oven and increase heat to 450 degrees. Sprinkle bread crumb mixture evenly on top of tomatoes.
  7. Bake gratin until bubbling and cheese are lightly browned, 5 to 10 minutes.
  8. Sprinkle with basil and let sit at room temperature 10 minutes before serving.

Provided by¬†America’s Test Kitchen