Zucchini Au Gratin Recipe (cheesy Zucchini Tian)

By Becky Hardin

Updated Feb 21, 2025

Zucchini Au Gratin Recipe is a great rice based side dish that’s perfect to serve throughout the holidays! You’ll love this deliciously cheesy zucchini casserole that can be made ahead of time. If you’re looking to use fresh seasonal zucchinis then my zucchini au gratin is the recipe you need!

Baked zucchini gratin in a black dish with a wooden spoon - 3

5-Star Reviews

“I can always use another zucchini recipe this time of year. This is a keeper!” -Tara

Zucchini Au Gratin Recipe

My zucchini casserole is a lighter version of Potato Au Gratin (no cream, no breadcrumbs) and a great way to use seasonal vegetables. (My Asparagus Au Gratin is another version). This baked casserole tastes rich and light at the same time and takes only 20 minutes to prepare.

Zucchini gratin is often cooked in tian (an earthenware baking dish) and sometimes called Zucchini Tian. The fresh grated squash, sautéed with caramelized onions and then combined with aromatic rice, is topped with Parmesan cheese and baked to perfection. It’s perfect for a holiday side dish !

Ingredients1x2x3x

▢ 2-2½ pounds zucchini yellow squash or a blend of yellow and green zucchini.
▢ 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
▢ 1¼ 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

Instructions

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

Prepare the zucchini

Cut off the stem and tip from each zucchini. Gently scrub the zucchini and peel. Note : If the zucchini is unpeeled, the color of the finished casserole will be much greener. 2-2½ pounds zucchini
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. Reserve this zucchini juice for later use. Place the squeezed zucchini on the prepared baking sheet and repeat until excess juice has been drained from all the grated zucchini. Cover the zucchini with 2 layers of paper towels and press down. Set the zucchini aside until ready to cook.

Prepare to assemble and bake

While the zucchini rests, cook the rice according to package directions minus 5 minutes less than directed. Remove the rice from the heat and stir. 1 cup uncooked long-grain white rice
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. 3 tablespoons olive oil, 1 cup diced onions
Add the minced garlic. Cook an additional 30 seconds and keep stirring. 2 large cloves garlic
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 stir for 2 more minutes. Remove from the heat. 3 tablespoons flour
Heat the milk and 1 cup reserved zucchini juice in the microwave (or stovetop just until warm). Add the milk/juice to the zucchini mixture and stir until incorporated. 1¼ cups whole milk, 1 cup reserved zucchini juice
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. 1 cup grated Parmesan cheese, Kosher salt and freshly ground black pepper
Transfer zucchini/rice mixture to greased dish, sprinkle evenly with reserved ¼ cup grated Parmesan and drizzle with olive oil. 2 tablespoons 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.)

Becky’s Tips

For richer decadent taste swap milk with cream.
Really squeeze the liquid out of your zucchini so you don’t have a runny gratin.
You can also use a mix of cheddar, Parmesan Reggiano and mozzarella cheese.

Nutrition information is automatically calculated, so should only be used as an approximation.

How to Store

Transfer any leftover gratin to an airtight container and refrigerate for up to 4 days. Reheat in the oven at 350°F covered with foil until bubbly.

I don’t recommend freezing, as dairy separates after the thawing process.

Zucchini gratin in a black baking dish with pieces served out of it - 4

Serving Suggestions

Baked zucchini casserole is a great recipe to serve with all of your favorite holiday meals. It is best served with Herb Crusted Rack of Lamb or delicious Beef Tenderloin Roast . To make a complete meal add a bowl of Tuscan Chicken Soup or some Roasted Vegetables for extra crunch!

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Zucchini Au Gratin Recipe