Zucchini and Onion Gratin with Herbed Breadcrumbs

It might seem less appropriate to cook zucchini when they’re as bright and bouncy as in the summer. And I don’t mean just lightly sear, but really cook — at a slow and low roast until meltingly tender — fresh, in-season zucchini. It might seem inappropriate to turn on the oven at all. But this aberration to my summer cooking routine has yielded a dramatically sweet, savory, and altogether satisfying way to enjoy one of my all-time favorite foods. It’s kind of like a slow-roasted vegetable crostini, only with the bread on top.

I didn’t grow up eating gratins. For a long time, I thought that meant there was cheese. And growing up, I did not like this substance at all — I didn’t even like macaroni and cheese, so I guess that makes me not truly an American, or a person, as some friends would see. It took being faced with a gratin recipe for just about every vegetable in Marcella Hazan’s exhaustive tome The Essentials of Italian Cooking to realize that gratins had more to do with texture, and that texture was often traditionally just breadcrumbs (“gratin” roughly translates to “bits and scrapings,” or gratings). That suited me better.

The texture could also come from simply baking ingredients in a shallow dish together until its exposed top formed a brittle crust. It could also come from cheese, baked such that it, too, solidified as a crunchy, golden helmet. The contents of the dish need not be excessively rich or creamy. That is a casserole, and I don’t think I’m qualified to speak on that.

sweet spring onions

It’s funny, because even long after making this, eating it, and washing its dishes, I still get phantom wafts of its sweet caramel, yet vegetal, odor. It’s like a cross between onions caramelizing in butter and someone making vegetable stock with the pot uncovered. Do you ever get smell-memories like that?

sage, rosemary, and a small sampling of houseplant herbs

drawing out moisture from the squash with salt

Butter aside, one of the best accents of this dish is the fresh drizzle of good olive oil that you can add just before serving. It really awakens the flavors and makes it feel more rich — even though it isn’t. A touch of creamy character however might just be achieved by the soft slips of zucchini instead, caught in the stage of still holding their moisture thanks to a low and steady cook, but having absorbed the sweetness of onions, and the savory herbaciousness of sage. Cooked just so, you could almost slick it onto a piece of toast like softened butter.

before baking


I’ve added an optional step of drawing out some of that moisture from the zucchini with salt first. This ensures a less watery (and more flavorful) outcome, but you could always keep cooking the gratin until its consistency satisfies. This recipe is also great for using up zucchini that’s maybe a little old, bruised, or looking a little weak. The rest you can save for the grill, or shaving up fresh.

Zucchini and Onion Gratin with Herbed Breadcrumbs
(makes 2-3 small servings)

2 lbs fresh zucchini or summer squash, or a combination
1 large yellow onion
1 cup fresh breadcrumbs (made from pulsing or pounding stale bread until coarse bits)
1-2 tablespoons fresh sage, finely chopped
1-2 teaspoons fresh rosemary, thyme, oregano, savory or marjoram, finely chopped
4-5 tablespoons extra-virgin olive oil
salt and freshly ground pepper to taste

Slice the zucchini and/or summer squash into thin rings about 1/8″. Spread them out on the board and sprinkle generously with salt. Let them stand at least 10 minutes to draw out moisture.

Slice the onions into even rings about 1/4″, or as uniformly as possible. Heat 2 tablespoons of the oil in a wide saucepan and add the onions along with a pinch of salt. Cook, stirring occasionally, 15-20 minutes, until onions are softened but not golden or brown. Reduce heat if any parts are browning. (Slicing them evenly helps ensure some don’t before others soften.) 

Preheat oven to 350 degrees. Grease a shallow, oven-safe casserole, gratin, or pie dish generously with olive oil. Toss the zucchini/summer squash with the cooked onions and a touch more olive oil, salt and black pepper to taste. Arrange in the bottom of the dish. In a small bowl, combine the breadcrumbs with the chopped herbs and a couple pinches of salt and pepper. Sprinkle the breadcrumb topping evenly across the vegetables. Bake for 30-35 minutes, or until the crumbs are golden and the edges of the vegetables are browning a little. Let sit for 5 minutes. Finish with an optional drizzle of olive oil on top and enjoy.

Cost Calculator
(for 2-3 servings)

2 lbs zucchini: $4.00
1 onion (from CSA): $0.50
1 cup fresh breadcrumbs (from leftover ends of baguette): $0.25
about 2 tablespoons chopped fresh herbs (from windowsill garden): $0.50
4-5 tablespoons olive oil, salt, pepper: $0.75

Total: $6.00

Health Factor

Three brownie points: This vegetable side makes an elegant summer snack, or an impressive addition to a party spread. Zucchini and summer squash are not lacking in the nutrition department, with lots of Vitamin C, B-vitamins, minerals, and even some protein. They’re very low in calories, though.

Green Factor

Nine maple leaves: I’m going to keep this one at the high streak that recipes have been enjoying here lately, because it’s a season of local abundance. The onions and zucchini — practically everything in this dish — were grown locally, the stale bread was leftover. This dish is vegetarian as well as vegan, easy on the environment, to boot.

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