Sheet Pan

Summer Squash Gratin

August 23, 2017
2 Ratings
Photo by Alexandra Stafford
  • Serves 6
Author Notes

A summer favorite: layers of roasted squash, parmesan cheese, and red bell pepper tomato sauce bake beneath a shroud of fresh bread crumbs—it's irresistible.

If you want to scale it back, follow this recipe: Zucchini Parmesan; if you want to use eggplant, see this post: No-Fuss Eggplant Parm —Alexandra Stafford

What You'll Need
  • For the red bell pepper-tomato sauce
  • 2 tomatoes, diced to yield about 2 cups
  • 2 red bell peppers, stemmed and seeded, diced to yield about 2 cups
  • kosher salt and fresh-cracked pepper to taste
  • 4 tablespoons unsalted butter or olive oil or a mix of the two
  • 1/4 cup fresh basil leaves
  • For the gratin
  • 4 pounds summer squash or zucchini, sliced thinly (between 1/8- and 1/4-inch thick), see notes above for scaling back
  • kosher salt and pepper to taste
  • 1/4 cup olive oil plus more for roasting
  • 3 cups fresh bread crumbs
  • 1 3/4 cups grated parmesan
  1. To make the sauce: Place peppers and tomatoes in a medium-sized saucepan or pot. Pour in 1/2 cup water and turn heat to high. Season with 1 teaspoon kosher salt and pepper to taste. Bring to a simmer, then turn heat down to medium high. Set a timer for 25 minutes. After about five minutes, the tomatoes and peppers will begin to release their juices, and the whole mixture should be bubbling. Adjust the heat if necessary so that the mixture stays at a constant bubble—medium to medium-high should do it. Stir every five minutes or so to make sure the tomatoes and peppers are not sticking to the bottom of the pan. If they are, add water by the 1/4 cup.
  2. When the peppers and tomatoes are tender and nearly all of the liquid has evaporated and the tomatoes and peppers are beginning to stick to pot, add the basil, butter, and/or oil to the pot, give it a stir, then transfer the contents of the pot to a food processor or blender. Blend until smooth. Taste. Adjust seasoning with more salt and pepper as necessary.
  3. To assemble the gratin: Preheat the oven to 450ºF. Arrange the sliced summer squash in single layers on rimmed sheet pans—you may need as many as three or more pans. Season with salt and pepper, drizzle each pan with at least 1 tablespoon olive oil (add more as needed), toss to coat, then spread into an even layer. Roast for 10 minutes or longer—you want to see some nice, dark coloring on the slices. Remove pans from oven and set aside. Note: If you roast three sheet pans at once, you may need to do some rearranging or to simply remove sheets as they are done — they all likely will not cook evenly. They may need as long as 15 to 20 minutes, too. Reduce oven to 400ºF.
  4. Meanwhile, make the breadcrumb topping: toss the breadcrumbs with the 1 cup grated parmesan cheese, 1/4 cup olive oil, 1/2 teaspoon salt and pepper to taste. Taste. If necessary, season with more salt or add more oil if crumbs seem dry. Set aside.
  5. Into a 9x13-inch baking pan, spoon in a small amount of sauce (about a heaping 1/2 cup or more), then add a single layer of squash, then a thin scattering of parmigiana (about 1/4 cup or so). Repeat until all ingredients are used, ending with a little sauce and cheese—you should have about 3 layers of squash. Top with the breadcrumb mixture.
  6. Bake until the mixture is bubbly and top is golden, 25 minutes or so depending on size of pan and thickness of layers. Remove from heat and allow to rest for 10 minutes before serving. This also tastes great at room temperature.

See what other Food52ers are saying.

  • Ikuko Miklowski
    Ikuko Miklowski
  • Alexandra Stafford
    Alexandra Stafford
  • Ashley
  • Regina Kanter-Cronin
    Regina Kanter-Cronin
I write the blog alexandra's kitchen, a place for mostly simple, sometimes fussy, and always seasonal recipes. My cookbook, Bread Toast Crumbs is available everywhere books are sold.

9 Reviews

Ikuko M. October 30, 2017
just made it - am in love ! oh dat sauce... :D ah ! thank you !
Alexandra S. October 30, 2017
So happy to hear this!
Ashley September 12, 2017
We tried this the other night and it was delicious! One question - can any part of the gratin be assembled ahead of time? And if so, how far ahead? Thanks!
Alexandra S. September 12, 2017
Hi Ashley,

Great to hear this! I'd imagine you can assemble the squash/sauce/cheese part at least 8 hours in advance if not more, but maybe not more than a day. And you can toss the crumbs with the cheese and olive oil in advance, too. I would refrigerate the mix in a ziplock bag. Bread stales faster in the fridge, but because you'll be packing them onto the squash and baking them, I think it's fine. Alternatively, toss the crumbs with the olive oil and salt, and leave those at room temperature (covered). Then toss with cheese right before baking. Good luck!
Regina K. September 4, 2017
Do you peel the tomatoes?
Alexandra S. September 4, 2017
Nope! It's super easy — just cut them into big chunks.
Marie F. September 3, 2017
Thank you---can't wait to try this!
Marie F. September 3, 2017
In the directions you don't specify how thinly the squash should be sliced. I don't have a mandolin. If the slices are too thin, I would imagine they might just disintegrate and become part of the sauce. Any suggestions?
Alexandra S. September 3, 2017
Good point! I'll edit now. I would slice them between 1/8 and 1/4 inch thick.