Zucchini Gratin

This Zucchini gratin is perfect to make in the summer time if you’re growing zucchini and needing ideas to eat it up. It’s also totally worth putting zucchini on your grocery list if you need to buy some to make this! The recipe comes from queen Ina Garten (with only very slight variation), and doesn’t disappoint with both flavor and simplicity. Sautéed zucchini and onions are wrapped up in a light creamy sauce and topped with cheesy breadcrumbs. It’s a great side dish to any grilled protein, feeling fresh in the summer and super cozy in the fall and winter. I love making this year round.

Ingredient Notes

  • Butter– Butter is used to caramelize the onions, adding flavor and richness.
  • Zucchini – While I’ve only made this with zucchini, it would be just as delicious with yellow winter squash, or a combination of the two, if you have both growing in your garden.
  • Onions – Any variety of onions will work. Sweeter varieties like Walla Walla or yellow onions caramelize particularly well due to their higher sugar content.
  • Salt and Pepper – I like to use kosher salt and fresh cracked black pepper
  • Ground nutmeg – nutmeg is a very common ingredient in white sauces. Don’t worry- it won’t make it taste like pumpkin pie!
  • Garlic– Fresh garlic adds tons of flavor here.
  • Flour – this recipe calls for all purpose flour
  • Milk – For the creamiest sauce, use whole milk. I recommend at least 2% for a richer consistency, though even 1% will work just fine.
  • Italian Style Breadcrumbs– This is a delicious technique where you mix grated cheese with breadcrumbs, creating a delicious crumbly, cheesy topping. These are dry breadcrumbs with Italian seasoning, usually sold in the baking aisle of the grocery store.
  • Gruyere – Look for gruyere by the fancier cheeses near the deli. Baby Swiss or muenster would be an ok substitute, if needed.

How to Make Zucchini Gratin

  1. This recipe starts with caramelizing some onions. This step takes the longest, so you will be able to prep your other ingredients while the onions cook down. You’ll caramelize them in a large skillet.
  2. While the onions are cooking, stir them every few minutes, but work on prepping the rest of the ingredients.  Slice zucchini t into 1/4 inch slices.  If your squash is pretty large, I’d slice it in half lengthwise first.  And if you have a mandoline, this is a great time to use it!  Those get tossed in the skillet after the onions are tender and starting to caramelize.  It’s important to use a large pan here because we need to get rid of a lot of moisture.  If the zucchini are crowded, they’ll just end up boiling and we want all of that excess water to evaporate so the dish isn’t watery.
  3. After the squash cooks down, add salt, pepper, a little garlic, and a pinch of nutmeg. 
  4. Cook that for a few minutes longer (your zucchini should be pretty tender at this point) and then add a little flour and milk to start the creamy sauce.
  5. Transfer mixture into a baking dish. 
  6. For the topping, combine some Italian flavored bread crumbs and some Gruyere cheese.
  7. Sprinkle it over the top of your baking dish. 
  8. Then just bake it in the oven for a few minutes and watch that cheese melt and the breadcrumbs toast to perfection. Definitely let it sit for a few minutes before serving to set up.


We love to eat this along with a great grilled steak for a perfect summer meal.  The zucchini gratin was hearty enough that we didn’t need much else.  Perfection!

Frequently Asked Questions

Can I make this ahead of time?

This is a recipe that’s best made fresh. If you really needed to, you could caramelize the onions ahead of time, slice your squash, and grate your cheese.

Can I make this with yellow zucchini or squash?

Yes, either option would be delicious.

Zucchini gratin in a white bowl

Zucchini Gratin

5 from 6 votes
Sliced squash and caramelized onions in a light cream sauce is topped with cheese and toasted breadcrumbs in this delicious zucchini gratin.
Prep Time 20 minutes
Cook Time 50 minutes
Total Time 1 hour 10 minutes
Servings8 servings

Equipment

Ingredients

  • 6 tablespoons butter
  • 1 pound yellow onions cut in half and sliced (about 3 large)
  • 2 pounds zucchini and/or yellow squash sliced 1/4-inch thick (about 4 medium zucchini)
  • 2 teaspoons kosher salt use 1/2 teaspoon if using table salt
  • ½ teaspoon freshly ground black pepper
  • ¼ teaspoon ground nutmeg
  • 2 cloves garlic finely minced or pressed
  • 2 tablespoons all-purpose flour
  • 1 cup warm milk
  • ¾ cup Italian style bread crumbs
  • ¾ cup grated Gruyere

Instructions

  • Preheat the oven to 400 degrees F.
  • Melt the butter in a very large sauté pan and cook the onions over low heat for about 20 minutes, or until tender but not browned.  As the onions are cooking, stir them occasionally and work on prepping the other ingredients.
  • Add the zucchini to the pan and cook, covered, for 8-10 minutes, or until tender. Add the salt, pepper, nutmeg, and garlic and cook uncovered for 5 more minutes, stirring often.
  • Whisk flour into the milk and add to pan, turning up heat slightly just until milk heats and starts bubbling.  Then cook over low heat for a few minutes, until it thickens and makes a sauce. Pour the zucchini mixture, and all the sauce into an 8 by 10-inch baking dish (or something close to that).
  • Combine the bread crumbs and Gruyere and sprinkle on top of the zucchini mixture. Drizzle a little olive oil over the top (place your finger over the opening of the bottle to make it easier to just drizzle a little) and bake for 20 minutes, or until bubbly and browned.  Cool for a few minutes before serving.

Notes

Recipe (with very minor changes) from Ina Garten.

Nutrition

Calories: 255kcal, Carbohydrates: 24g, Protein: 8g, Fat: 15g, Saturated Fat: 9g, Polyunsaturated Fat: 1g, Monounsaturated Fat: 4g, Trans Fat: 0.3g, Cholesterol: 45mg, Sodium: 820mg, Potassium: 442mg, Fiber: 3g, Sugar: 7g, Vitamin A: 657IU, Vitamin C: 25mg, Calcium: 198mg, Iron: 1mg
Course: Side Dish
Cuisine: American
Keyword: zucchini gratin
Calories: 255kcal
Author: Our Best Bites, adapted from Ina Garten
Did You Make This Recipe?Snap a picture, and hashtag it #ourbestbites. We love to see your creations on our Instagram @ourbestbites!
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Meet The Author

Sara Wells

Sara Wells co-founded Our Best Bites in 2008. She is the author of three Bestselling Cook Books, Best Bites: 150 Family Favorite RecipesSavoring the Seasons with Our Best Bites, and 400 Calories or Less from Our Best Bites. Sara’s work has been featured in many local and national news outlets and publications such as Parenting MagazineBetter Homes & GardensFine CookingThe Rachel Ray Show and the New York Times.

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Questions & Reviews

  1. 5 stars
    Served this delicious zucchini gratin with salmon and Our Best Bites Fresh Sweet Corn Salad. A perfect summer meal–the only thing we were missing was watermelon. I used Panko bread crumbs and added Italian seasonings since I didn’t have Italian breadcrumbs. Everyone loved this dish and I will make it again.

  2. 5 stars
    Made this today for lunch and loved it! I added some goat cheese to the sauce because I had some handy. Delicious!

  3. Just wondering if you really cook the onion for 20 min. I made this tonight and it turned out wonderfully, but I did not cook the onion for more than 2 or 3 min.

  4. I have to be honest, we’re not very creative around our house when it comes to veggies. We mostly do boring stuff like mashed potatoes, corn, green beans…yada, yada, yada. Well, I just have to say thank you, because this recipe surprised me, it was really tasty. It’s given me the confidence to try more vegetable recipes. Wish me luck!:)

  5. There is no such thing as too many ways to use up garden produce, especially when made in a bestbites-worthy fashion. Thank you thank you and keep em comin! Can’t wait to try this one!

  6. 5 stars
    This is so yummy! I love how the nutmeg enhances the zucchini & pepper. My 1 & 4 year old ate it right up! I have made it twice in the past week & plan on making it again tonight. I couldn’t find the cheese but substituted 1/4 cup each of parmeasan & Swiss, added about a 1/4 cup of a colby jack blend that I had on hand & it turned out amazing! Thank you for such a delicious recipe.

  7. I wish I had a garden with an over abundance of veggies, but luckily I have lots of generous friends who do and they willing share! This looks absolutely delicious!

  8. 5 stars
    This is delicious! I made a special trip to get the Gruyere, and boy oh boy, and I glad I did! It really made this over the top. Even my zucchini hating son ate it up.
    May I suggest moving the instruction to pre-heat the oven to after the onions are done? My oven was on for almost an hour by the time I was done, and that really heated up the kitchen.

  9. 5 stars
    I made this for dinner tonight and my husband loved it! Mine turned out a little watery but it still tasted delicious. Thanks for the great recipe!

    1. That’s weird it turned out a little watery, mine wasn’t watery at all. You might have had an extra juicy zucchini or needed to cook the sauce a bit longer. But I’m glad it was delish!

  10. 5 stars
    I added ground beef and made it a main dish. Also subbed parmesan cheese because I had it on hand…AMAZING!! Definitely a keeper in our house!

    1. That’s such a good idea; I was thinking it would be really good with some chopped ham or Italian turkey sausage; I’ll have to try that next time!

  11. Just prepped this with my littles this afternoon with veggies they picked from our garden. Waiting to go into the oven in a little bit for dinner. Feel free to keep the zucchini recipes coming!

  12. I think I’ll eat any vegetable covered in cheese, especially gruyere!!! Yum!

    Miss you both!

  13. What a great idea! Can’t wait to try this! I’m always looking for new ways to cook veggies! Pinned!

  14. oh, I have another question… 🙂 I don’t have Italian style bread crumbs. But I do have a lot of Panko bread crumbs. Could I just mix in a few shakes of the McCormick Italian seasoning into the Panko crumbs to get the same affect? Or do you think it would alter the dish too much? Thanks…

  15. I have to laugh – on the one hand, this dish sound delicious. I love anything made with zucchini, but ironically, can’t have a garden to produce them. On the other hand – like I said in my own blog recently: Preheat oven to 400 degrees. Seriously? (Don’t you know how hot it is already?)LOL

    1. I think it depends on where you live. It’s hot here, but because of that my AC is pumping and my house is super cold. I sometimes wear a light sweatshirt inside and baking doesn’t phase me!

  16. Never too many zucchini recipes!! My garden is doing great and I am always looking for new ways to cook zucchini, eggplant, peppers, butternut squash and tomatoes!! (Hint hint hint)

  17. Yum, this sounds incredible! We got about 10 pounds of zucchini out of our garden today. Can’t wait to try this!

  18. No garden (yet), but I expect zucchini in our CSA box next week 🙂

    Btw, would you gals consider posting a mandoline tutorial? I have one but I am bad at it…

    1. Marnie- what kind of problem do you have with your mandoline? You should be able to just easily slice, slice, slice!

  19. Is this watery? I made something like this before and the zucchini had so much liquid after it baked – I had to drain it on a paper towel – haha

    1. Nope, not watery at all. If you were to put raw zucchini in there, I can see how that could be a problem, but saute gets rid of extra moisture and what’s left creates a sauce.

  20. This looks wonderful! Since aged cheeses like Gruyere contribute to my migraines, do you think Mozzarella or Monterey Jack would do? They aren’t aged the same, but certainly don’t have the rich flavor either… Any other suggestions?

  21. Sigh. We just moved from MN (where I had 30 square feet of garden, which included moe zucchini than I could handle) to Charlotte NC, where my garden barely exists and was started too late anyway for much yield. I’m dying over here- and your awesome recipe is not helping! LOL!

  22. I actually think I have all the ingredients for this right now. That doesn’t happen very often. Dinner…planned. This looks like another delicious way to enjoy zucchini. Thanks.