Summer squash gratin with tomato-red pepper sauce

Are you looking to use up a giant pile of zucchini or summer squash? Say, four pounds of it? This recipe is just the ticket. It’s a simple yet flavor-packed vegetarian gratin, made up of squash slices layered with tomato-pepper sauce and Parmesan cheese, then topped with oil-slicked breadcrumbs. This is what I think of as summer comfort food: crisp and golden on top, bright and fresh-flavored underneath. Plus there’s cheese.

The real secret sauce of this gratin is…well, the sauce. It is one of those simple-yet-spectacular marvels of summer cooking: tomatoes and red bell peppers, simmered with a splash of water until they’re very soft, then blended with a knob of butter and a handful of fresh basil leaves. (You could use olive oil instead of butter, or a mix of the two.) Somehow, those few ingredients produce a rich orange-red sauce that’s creamy-without-cream and packed with bright flavor.

Of course, the sauce is outrageously delicious in this gratin. Tomato, pepper, squash, and basil is a can’t-fail flavor combination. But once you taste this stuff, you’ll want to make extra next time. It’s fabulous over pasta or as a marinara-like dip, and I can only imagine how great it’d be draped over chicken Parmesan. It also freezes beautifully, so you could double the batch while prepping this gratin and save the leftovers for another day.

tomato pepper sauce

I tweaked this from a Food52 recipe, which calls for roasting the squash before assembling the gratin. I don’t own enough baking sheets to fit four pounds of sliced squash in a single layer, and I didn’t love the idea of shuffling baking sheets in and out of a very hot oven during the height of summer. So I skip the roasting step altogether, and I don’t really miss it. The flavor of the squash is fresher, and the slices stay firmer and more intact. (A lot of folks–myself included–are averse to the mushiness of fully-cooked zucchini, so I slice my squash on the thicker side for a crisp-tender final texture.)

The roasting step does serve one important purpose, however. It drives off excess liquid from the squash, which would otherwise make the gratin soggy. My solution is to salt-purge the squash instead. After slicing the squash, I toss it with a generous dose of kosher salt, then let it drain in a colander until it softens and gives up a shocking amount of liquid. Then I pat the squash dry, and it’s ready to be layered with sauce and blanketed with breadcrumbs.

squash gratin w tomato pepper sauce

Tomato-Red Pepper Sauce (makes about 2 cups)

From Food52

Note: This makes enough for the gratin recipe below, or enough to sauce 3/4 lb (12 oz) dried pasta. Feel free to double or even triple the recipe if desired–the extra sauce will keep, tightly covered, in the fridge for up to 3 days or the freezer for up to 2 months.

2 large ripe tomatoes (about 3/4 lb), diced

2 red bell peppers (about 1/2 lb), seeded and diced

1/2 cup water, plus more as needed

Salt to taste

1/4 cup (4 tbsp) unsalted butter, olive oil, or a combination

1/4 packed cup fresh basil leaves

Freshly ground black pepper to taste

In a large saucepan, combine tomatoes, peppers, water, and a large pinch of salt. Bring to a boil over medium-high heat, then reduce the heat to medium. Cook, uncovered and stirring occasionally, for 25-30 minutes, until the vegetables are very soft and starting to stick to the bottom of the pot. If the vegetables start sticking before the 25-minute mark, add a splash of water.

Stir in butter and/or oil and basil. Transfer the sauce to a blender (or use an immersion blender) and blend until smooth. Taste and season with salt and pepper. Use immediately, or let cool and transfer to an airtight container. The sauce will keep in the refrigerator for up to 3 days, or in the freezer for up to 4 months.

Summer Squash Gratin (serves 6-8)

Adapted from Food52

Note: To make this gluten-free, use gluten-free bread to make fresh breadcrumbs. I’m also told that gluten-free panko breadcrumbs exist, though I have not seen them in stores.

4 lb zucchini or summer squash

1 tbsp kosher salt or coarse sea salt

3 cups fresh (homemade) breadcrumbs OR 2 cups panko breadcrumbs (see note)

2 cups tomato-pepper sauce (see recipe above)

1/4 cup olive oil

2 cups finely grated Parmesan cheese

Freshly ground black pepper to taste

Trim the ends off the squash and cut them into rounds about 1/4 inch thick. (If you prefer your zucchini softer, cut the slices closer to 1/8 inch thick.) I do this with a knife, but feel free to use a mandoline or slicer if you’ve got one.

In your largest mixing bowl, combine squash slices and 1 tbsp salt, and toss until thoroughly combined. Transfer to a colander and let the squash slices drain for about 30 minutes, or until they’ve given up a lot of liquid and become soft and pliable. Blot off as much of the excess moisture as you can with paper towels.

Preheat the oven to 400º F and position a rack in the middle. Grease a 9×13 pan, and line a baking sheet with foil to catch any bubble-overs. In a medium mixing bowl, combine breadcrumbs, olive oil, and half the Parmesan cheese. Toss to combine, and set aside.

Spread about 1/2 cup sauce over the bottom of the greased baking dish. Lay down 1/3 of the squash slices, grind over some black pepper, and scatter over a handful of Parmesan. Repeat the layering process–sauce, squash, pepper, cheese–two more times. Spread over the rest of the sauce and scatter over any remaining Parmesan. Top with breadcrumbs.

Place the baking dish on the lined baking sheet. Bake for 25-30 minutes, until the top is golden and the juices are bubbling. Remove from the oven and let rest for at least 10 minutes. Serve warm or at room temperature.

Make ahead: You can assemble the gratin, minus the breadcrumbs, up to 24 hours in advance. Cover the pan and refrigerate, then take it out of the fridge about 1 hour before you’re ready to bake. Wait until just before baking to add the breadcrumb mixture, so that it stays as crisp as possible.

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