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zucchini gratin in pan with wooden spoon

Zucchini Au Gratin Recipe

Course: Side Dish
Cuisine: American
Prep Time: 20 minutes
Cook Time: 1 hour
Total Time: 1 hour 20 minutes
Servings: 8 people
Calories: 282kcal
This delicious Zucchini Au Gratin Recipe is a great rice based side dish that's perfect to serve throughout the holidays.  This amazing zucchini casserole is deliciously cheesy and can be made ahead of time.
Print Recipe


  • 2-2½ pounds zucchini yellow squash or a blend of both
  • 1 cup uncooked long-grain white rice NOT Minute Rice
  • 1 cup diced onions
  • 3 tablespoons olive oil
  • 2 large cloves garlic minced
  • 3 tablespoons flour
  • cups whole milk
  • 1 cup reserved zucchini juice
  • 1 cup grated Parmesan cheese divided
  • Kosher salt and freshly ground black pepper to taste
  • 2 tablespoons olive oil


  • Spray a large (8-10 cucasserole dish with nonstick cooking spray.
  • Heat oven to 400°F and position oven rack to upper third position.

To prep the zucchini:

  • Cut off the stem and tip from each zucchini. Gently scrub the zucchini and peel, if desired (important if using larger, tougher zucchini). *See note.
  • If available, use a food processor to grate the zucchini. If a food processor isn’t available, rub the zucchini against the coarse side of a grater. Place the grated zucchini in a large colander set over a large bowl. Sprinkle 1-teaspoon kosher salt over the zucchini and toss together until mixed thoroughly. Allow the squash to drain at least 10 minutes (or even overnight (covered). Line a large baking sheet with 3 layers of paper towels. Remove the colander from the bowl and squeeze the grated zucchini, one handful at-a-time, over the bowl with the reserved zucchini juice. Place the squeezed zucchini on the prepared baking sheet and repeat until excess juice has been drained from all the zucchini. Cover the zucchini with 2 layers of paper towels and press down; set the zucchini aside until ready to cook.
  • While the zucchini rests, cook the rice according to package directions EXCEPT cook the rice 5 minutes less than directed. Remove the rice from the heat and stir.
  • While the rice cooks, heat a large skillet over medium-low heat and add 3 tablespoons oil. When the oil is hot, add the diced onion and cook 8-10 minutes or until tender, translucent and beginning to brown lightly.
  • Add the minced garlic and, while stirring, cook an additional 30 seconds.
  • Add the dried zucchini and mix well. Cook 5-6 minutes or until the zucchini is almost tender.
  • Sprinkle the zucchini with the flour and mix well. Cook (and sti2 more minutes. Remove from the heat.
  • Heat the milk and 1 cup reserved zucchini juice in the microwave (or stovetojust until warm. Add the milk/juice to the zucchini mixture and stir until incorporated.
  • Set the pan over medium-low heat and add the par-cooked rice. Stir and cook about 5 minutes or until most of the excess liquid has reduced. Watch closely so it doesn’t scorch.
  • Remove from the heat and add ¾ cup grated Parmesan cheese. Stir well and season to taste with kosher salt & freshly ground black pepper, if needed.
  • Transfer zucchini/rice mixture to prepared dish, sprinkle evenly with reserved ¼ cup grated Parmesan and drizzle with olive oil.
  • Bake 30-40 minutes at 400°F or until bubbly throughout and top is golden brown. (If the casserole looks heated through and bubbly, but the top is still somewhat pale, set the oven to broil and cook another 2-3 minutes. Watch very closely until the zucchini is golden brown and gorgeous on top.
  • Enjoy!


Adapted slightly from Food52, Julia Child’s Zucchini Tian: https://food52.com/blog/4236-julia-child-s-zucchini-tian
*Note: If the zucchini is unpeeled, the color of the finished casserole will be much greener


Calories: 282kcal | Carbohydrates: 29g | Protein: 10g | Fat: 14g | Saturated Fat: 4g | Cholesterol: 15mg | Sodium: 221mg | Potassium: 492mg | Fiber: 2g | Sugar: 6g | Vitamin A: 453IU | Vitamin C: 27mg | Calcium: 217mg | Iron: 1mg