Cheesy Zucchini Gratin (Low Carb)

This cheesy zucchini gratin is rich, savory, and comforting, and it happens to be low carb too. Tender sliced zucchini and caramelized onion simmer in a garlicky cream and Parmesan sauce, then get topped with a generous layer of melty cheese and baked until golden and bubbly. It’s everything you want in a gratin, creamy, cheesy, deeply savory, and satisfying, made with simple ingredients and ready in well under an hour. Whether you’re cutting carbs or just want a delicious, cozy side dish, this one delivers big flavor from a humble vegetable.

The genius of this gratin is how it transforms zucchini, often a bland or watery vegetable, into something rich and craveable. Caramelizing the onion builds sweetness, garlic and beef broth add savory depth, and heavy cream and Parmesan turn it all into a luscious sauce that the zucchini soaks up as it cooks. A final layer of melty cheese on top, baked until golden, gives you that satisfying gratin crust. It’s a fantastic way to make a vegetable side feel special.

Why this works

A few simple techniques are what give this gratin its rich flavor, and they’re worth understanding.

Caramelizing the onion builds a sweet, savory base. Cooking the onion slowly in butter until lightly caramelized develops its natural sweetness and savory depth, which forms the foundation of the whole dish. Adding the garlic after (rather than with the onion) keeps it from burning while still infusing the dish with its flavor.

The broth and cream create a rich, savory sauce. Beef broth adds deep, meaty flavor, while heavy cream makes the sauce luxuriously rich and helps it cling to the zucchini as it cooks. Parmesan stirred into the simmering liquid melts in and adds salty, nutty, savory depth, essentially building a quick, flavorful cream sauce right in the skillet. It’s the same basic idea behind a classic potato gratin, just adapted to a lighter, faster-cooking vegetable.

Cooking the zucchini directly in the sauce is key. Adding the sliced zucchini to the bubbling cream mixture and simmering it until just softened lets it absorb all that savory flavor while releasing a little of its own moisture, which helps thicken the sauce further. This is what makes the zucchini taste rich rather than watery.

And the cheese topping is what makes it a true gratin. A generous, even layer of melty cheese (mozzarella and asiago are a great combo) over the top, baked at high heat until golden and bubbling, creates that classic gratin crust, gooey underneath and deeply browned on top. Baking it hot and relatively quick keeps the zucchini from overcooking while still getting a beautifully golden top. That contrast between the browned, slightly crisp cheese and the soft, saucy vegetable underneath is really the whole point of a gratin, whatever vegetable it’s built on.

What goes in

The ingredient list is short and rich.

this now & bake later ❤️

You’ll need zucchini, freshly grated Parmesan cheese, butter, an onion, beef broth, cheese of your choice (mozzarella and asiago is a great combo), garlic, salt and pepper, and heavy cream.

A few notes. Slice the zucchini thin and into half-moons so it cooks evenly and absorbs the sauce. Use freshly grated Parmesan rather than pre-shredded for the smoothest melt. For the topping cheese, mozzarella and asiago give great meltiness and flavor, but any good melting cheese works. And use beef broth for a deeper, savory flavor (chicken or vegetable broth would work as a lighter substitute).

How to make it

In a large ovenproof skillet, melt the butter with the onion and cook until the onion is lightly caramelized. Add the minced garlic and sauté for about 1 minute over medium heat.

Add the beef broth, salt, pepper, and heavy cream to the onion and garlic mixture, and stir to combine.

Let it begin to bubble slightly, then stir in the Parmesan cheese.

Add the sliced zucchini and cook for an additional 5 minutes, until softened.

Top evenly with your cheese of choice across the entire surface. Bake at 425°F for about 12 to 15 minutes, or until the cheese is browned to your liking.

Serve hot.

Tips, serving, and storing

A few things help. Caramelize the onion patiently for the best flavor base, don’t rush it. Use a good ovenproof skillet so you can go straight from stovetop to oven. Slice the zucchini evenly so it cooks at the same rate. And keep an eye on the broiler-level heat toward the end so the cheese browns without burning.

A couple more. If your zucchini releases a lot of liquid as it cooks, you can simmer it a bit longer before adding the cheese to let some of that liquid reduce. And a sprinkle of fresh herbs (thyme or parsley) on top after baking adds a nice fresh finish.

This gratin makes a wonderful side dish for steak, chicken, pork chops, or roasted meats, and it’s hearty enough to serve as a light vegetarian main with a salad on the side. It’s especially great for low-carb or keto meals in place of potatoes or pasta gratins. Serve it hot, straight from the oven, while the cheese is still bubbly and golden.

For storing, keep leftovers in an airtight container in the fridge for up to 3 days. Reheat in the oven or a skillet to help the cheese re-melt and the texture stay good (the microwave works too, though the top won’t be as crisp). Because zucchini releases moisture as it sits, leftovers will be a bit softer and saucier than fresh, still delicious, just less crisp on top. I wouldn’t recommend freezing this one, as the texture of the zucchini and cream sauce can suffer.

This makes about 4 servings as a side. Rich, cheesy, savory, and comforting, this low-carb zucchini gratin proves a humble vegetable can be the star of the plate, and it’s a great way to use up extra zucchini in the most delicious way possible. It also happens to make a convincing case for anyone who’s written zucchini off as boring, since almost nothing about this dish reads as diet food.

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