Zucchini & Caramelized Onion Gratin

Zucchini & Caramelized Onion GratinI’m not entirely sure which is more abundant this time of year, zucchini or zucchini recipes.  And with that said, this is my contribution to the year’s zucchini files.

I’m standing tall and proud next to my contribution–this gratin is so delicious I’ll be tempted to devote next year’s garden entirely to zucchini!  Thin rounds of zucchini are layered and baked with caramelized onions and creamy Fontina cheese.  Breadcrumbs and Parmesan add a crispy, nutty layer of flavor to the top and bottom and a smattering of olives and/or anchovies adds a salty briny-ness that counters the sweet onions.

Nothing about my gratin is difficult to make but I would encourage you to take your time while making it.  I cooked the onions low and slow for almost an hour. While I was waiting for them to caramelize, I sliced my zucchini thin, tossed it with salt, and let it drain in a colander.

When your onions are finished, start assembling the gratin.  Smear a pie plate with olive oil and dust with breadcrumbs.  Make a base with zucchini, gently blotting the slices with a paper towel before adding them to the pan.  Spread some of the onions over the zucchini, then sprinkle with grated cheese.  Repeat.  Finish with a final layer of zucchini topped with breadcrumbs and Parmesan.  Top with a smattering of anchovies or black olives (depending on who’s coming to dinner!) and bake.

Unbaked Zucchini Gratin

The gratin is rich but not over-the-top, pretty but not too fussy, good hot and even better around room temperature.  It’ll make a zucchini-lover out of any zucchini-hater or merely the zucchini-indifferent and have you hoping for zucchini well into September.

Zucchini, Caramelized Onion & Anchovy Gratin

Zucchini & Caramelized Onion Gratin
Prep time
Cook time
Total time
If you'd like to turn the zucchini gratin from side dish to main, you could add a layer of eggplant and serve it with a simple tomato sauce.
Recipe type: Vegetable, Side Dish
Cuisine: Summer, Italian
Serves: 6-8
  • 2 Tbsp. Butter
  • 2 Tbsp. Olive Oil, plus more for the pan
  • 3 large Yellow Onions, thinly sliced
  • 1 tsp. fresh Thyme
  • 5 medium Zucchini, very thinly sliced (I used my mandoline set at ⅜ in.)
  • ¾ c. Breadcrumbs
  • 1½ c. grated Fontina Cheese
  • ¼ c. Parmesan Cheese
  • about 12 Anchovies OR a handful of flavorful Black Olives
  1. In a large, wide sauté pan, melt the butter and olive oil together over medium-low heat. Add the sliced onion and slowly cook until the onions are golden and caramelized, about an hour. Season with salt, pepper, and the fresh thyme.
  2. While the onions are cooking, place the sliced zucchini in a large colander and toss with a scant teaspoon of kosher salt. Set the colander over the sink and allow the zucchini to drain while you wait for the onions, tossing periodically.
  3. Preheat the oven to 400°. Generously rub a pie plate with olive oil. Add about ¼ c. of the breadcrumbs and shake them around until the pan is well coated. Now start building the gratin. Have a few paper towels handy and gently blot the moisture off the zucchini as you work (soggy zucchini dishes are the reason lots of people think they hate zucchini!). Make a base layer of overlapping zucchini slices. Spread with about ½ of the caramelized onions, sprinkle with about ½ of the Fontina, and repeat. Finish with a layer of zucchini. Sprinkle with the breadcrumbs and Parmesan, then drizzle with a little olive oil. Top with anchovies or olives.
  4. Cover the gratin with a sheet of foil with holes poked in it, taking care that the foil does not touch the cheese. Bake until the zucchini is tender when poked with a sharp knife, about 35 minutes. Remove the foil and bake for another 5 minutes to crisp up the topping. Allow to cool for a few minutes before serving or cool to room temperature.


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  1. pam says

    I can vouch for this one – thanks for letting me be a “taster”! It is delicious and I am craving more….hint, hint!

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