Kohlrabi au Gratin (Classic French-Style Bake)

Au gratin is a French technique, not a dish. It means “by scraping” — a reference to the crust you scrape off the dish when serving. The defining feature is a golden, broiled top layer, usually built from cheese, breadcrumbs, or both, set over vegetables bound in béchamel sauce.

Most people know au gratin from potatoes. But the technique works with almost any vegetable that holds its shape during baking, and kohlrabi is arguably a better candidate than potatoes for the French treatment. It absorbs béchamel without turning starchy. It keeps a clean, slightly sweet flavor that doesn’t compete with Gruyère. And it holds a gentle bite after 30 minutes in a hot oven — no collapsing into mush.

If you’re already familiar with what kohlrabi tastes like, you’ll understand why it works here. That mild, broccoli-stem sweetness pairs naturally with nutmeg-scented cream sauce and salty, melted cheese.

Au Gratin vs. Regular Gratin: What’s the Difference?

The terms get used interchangeably in English, but in French cooking there is a distinction worth noting.

A gratin is any baked dish with a browned top. That top can be cheese, breadcrumbs, egg, or just the natural browning of whatever’s in the dish. Gratin dauphinois — the famous potato dish from the Dauphiné region — traditionally uses no cheese at all, just cream, garlic, and potatoes.

Au gratin specifically implies a crust formed from grated cheese and often breadcrumbs, broiled or baked until crisp. It’s a subset of gratin technique, and it’s the version most associated with the golden, bubbling dishes that come out of restaurant kitchens.

For kohlrabi, the au gratin approach — béchamel, cheese, breadcrumbs — produces the best result. The béchamel binds everything together and compensates for kohlrabi’s lack of starch, while the breadcrumb-cheese crust gives you that essential contrast between creamy interior and shattering top.

Classic Kohlrabi au Gratin Recipe

This serves 4–6 as a side dish. It’s straightforward enough for a weeknight but elegant enough for a dinner party.

Ingredients

For the kohlrabi:

• 4 medium kohlrabi (about 2 pounds total), peeled and sliced 3mm thick
• 1 tablespoon butter for greasing
• Salt for blanching water

For the béchamel:

• 3 tablespoons unsalted butter
• 3 tablespoons all-purpose flour
• 2 cups whole milk, warmed
• 1/4 teaspoon freshly grated nutmeg
• 1/2 teaspoon fine salt
• 1/4 teaspoon white pepper

For the gratin topping:

• 150g Gruyère, finely grated
• 40g fresh breadcrumbs (from day-old bread, not panko)
• 1 tablespoon melted butter
• 1 tablespoon fresh thyme leaves (optional)

Instructions

Step 1: Prepare the kohlrabi

Peel the kohlrabi generously — you want to get past the fibrous outer layer into the tender interior. For a guide on technique, see our piece on how to peel and prepare kohlrabi. Slice into rounds about 3mm thick. A mandoline is ideal here; uniform thickness matters for even cooking.

Bring a large pot of well-salted water to a boil. Blanch the kohlrabi slices for 3–4 minutes, until they’re just barely tender when pierced with a knife. You’re not cooking them through — they’ll finish in the oven. Drain and spread on a clean towel to dry.

This blanching step is important. Raw kohlrabi takes a long time to soften in the oven, and by the time it’s tender, your béchamel has broken and your topping has burned. Par-cooking solves the timing problem.

Step 2: Make the béchamel

Melt the butter in a medium saucepan over medium heat. Add the flour and stir constantly for 2 minutes — you want a pale roux, not a brown one. The flour should smell faintly nutty but not take on any color.

Gradually pour in the warm milk, whisking continuously. Add it in three or four additions, whisking each one smooth before adding more. This prevents lumps. If you dump all the milk in at once, you’ll spend the next ten minutes trying to whisk out clumps.

Cook the sauce over medium heat, stirring often, until it thickens enough to coat the back of a spoon — about 5 minutes. Season with nutmeg, salt, and white pepper. Take it off the heat.

The sauce should be the consistency of heavy cream, maybe slightly thicker. It will thicken further in the oven.

Step 3: Assemble

Preheat your oven to 190°C (375°F).

Butter a gratin dish or shallow baking dish (roughly 20x30cm). Layer half the kohlrabi slices, overlapping slightly. Spoon over half the béchamel. Scatter over a third of the Gruyère. Repeat with the remaining kohlrabi, remaining béchamel, and another third of the Gruyère.

For the topping, toss the breadcrumbs with the melted butter and remaining Gruyère. Spread evenly over the dish. Scatter the thyme leaves on top if using.

Step 4: Bake

Bake for 25–30 minutes, until the sauce is bubbling around the edges and the top is golden. If the topping isn’t as brown as you’d like, run it under the broiler for 2–3 minutes. Watch it closely — breadcrumbs go from golden to charred in about 30 seconds.

Let the dish rest for 10 minutes before serving. This allows the sauce to set slightly, so the portions hold together when you cut into them rather than flooding the plate.

Variations on the French Theme

Kohlrabi au Gratin with Comté

Swap the Gruyère for Comté — a French alpine cheese with a slightly sweeter, more complex flavor. Comté is the most-consumed cheese in France and is arguably the better match for kohlrabi’s mild sweetness. Use the same quantity and technique.

Kohlrabi au Gratin with Leeks

Slice 2 large leeks (white and light green parts only) into thin rounds. Sauté in butter until soft, about 8 minutes. Layer the leeks between the kohlrabi layers. Leeks and kohlrabi are a classic combination in French vegetable cooking — the sweetness of cooked leeks amplifies the sweetness of the kohlrabi.

Kohlrabi au Gratin with Mustard

Whisk 2 tablespoons of Dijon mustard into the béchamel just before assembling. Mustard and Gruyère is one of the great French flavor pairings, and it adds a sharpness that cuts through the richness of the cream sauce.

Lighter Version with Crème Fraîche

Skip the béchamel entirely. Thin 200ml crème fraîche with 100ml milk, season with nutmeg, salt, and pepper, and use this as your sauce layer. The result is lighter and tangier. You lose some of the binding quality of béchamel, so the finished dish will be a bit more loose, but the flavor is excellent.

Why Kohlrabi Suits the Au Gratin Treatment

Three properties make kohlrabi unusually well-suited to this technique.

Structure. Kohlrabi slices don’t fall apart. After 30 minutes of baking in cream sauce, they still hold their shape and maintain a slight bite. You can slice portions cleanly. Zucchini, by contrast, turns to mush. Potatoes lose their edges. Kohlrabi keeps its composure.

Neutral flavor. The best au gratin vegetables are the ones that let the sauce and cheese do the talking. Kohlrabi’s flavor is mild — present but not assertive. It tastes good without demanding attention, which means the béchamel, the Gruyère, and the toasted breadcrumbs all come through clearly.

Low carb content. Kohlrabi has roughly a quarter of the carbohydrates of potatoes. The nutritional profile is worth checking if this matters to you — one cup of raw kohlrabi has about 8 grams of carbs versus 26 grams for the same amount of potato. An au gratin made with kohlrabi instead of potatoes is genuinely lower in carbohydrates without tasting like a compromise.

Serving Suggestions

Kohlrabi au gratin works as a side dish with:

• Roast chicken. The classic pairing. A simply roasted bird with a golden gratin on the side is a complete French meal.
• Pan-seared fish. Something mild — sole, cod, halibut. The gratin’s richness complements lean protein.
• Grilled lamb chops. The Gruyère and lamb pairing is underrated. A few chops with this gratin and a green salad is an excellent dinner.
• As a main course. For a vegetarian dinner, serve a generous portion with a bitter green salad dressed in vinaigrette. The richness of the gratin against the sharpness of the greens works beautifully.

Tips for the Best Result

Slice thin and even. 3mm is the target. Thicker slices won’t cook through evenly; thinner ones lose their texture and turn papery. A mandoline makes this easy.

Warm the milk. Cold milk added to hot roux creates lumps. Warm it in a separate pan or in the microwave before whisking it in.

Don’t skip the blanching. Raw kohlrabi in a gratin dish takes 45+ minutes to become tender, by which point the sauce has separated and the topping is black. Three minutes of blanching solves this.

Use fresh breadcrumbs. Panko works in a pinch, but fresh breadcrumbs made from day-old bread (torn and pulsed in a food processor) create a finer, more cohesive crust that browns more evenly. This is the French way.

Rest before cutting. Ten minutes of resting after the oven is the difference between a neat slice and a pool of sauce on the plate.

Make-Ahead and Storage

Assemble the gratin up to 24 hours in advance — layer everything in the dish, cover with plastic wrap, and refrigerate. Add the breadcrumb topping just before baking. You’ll need to add 10–15 minutes to the baking time since the dish will be cold.

Leftovers keep for 3 days in the fridge. Reheat in a 180°C oven for 15 minutes, loosely covered with foil. The topping won’t be as crisp as the first time, but the flavors actually improve overnight as the béchamel absorbs into the kohlrabi.

Kohlrabi au gratin doesn’t freeze well. The béchamel tends to separate and turn grainy when thawed. If you want to freeze kohlrabi for other uses, do it before assembling the gratin, not after.