Celeriac and Parmesan gratin is comfort food with a touch of fancy

Celeriac, also known as celery root, is a versatile root vegetable that looks like a turnip, but (perhaps unsurprisingly) has a subtle celery flavor. It can be a great lower calorie substitute for potatoes, though in the case of this recipe for a unique gratin, those potatoes aren’t going anywhere.

If you like celeriac, we recommend making extra of the delicious puree—it can be used for more than just this gratin. I like it spread on sourdough toast with a fried egg and pickled onions. It’s good to have in the fridge.

Can’t find celeriac at your local grocery store? Carrots, turnips or even butternut squash would all make great substitutes in the puree. Add a pinch of celery seed to retain the celery flavor.

Celeriac and Parmesan Gratin

Serves 6 to 8 people

Celeriac puree

Cook time: 1 hour (15 minutes active)

• 2 medium celeriac roots, peeled, ½-inch dice
• 1 quart whole milk
• 10 ounces Parmesan cheese, grated
• 2 sweet onions, ½-inch dice
• 6 to 8 cloves garlic, peeled and smashed
• ¼ cup butter, ½-inch dice
• ½ teaspoon lemon zest, microplaned
• ¼ teaspoon ground nutmeg
• ¼ teaspoon ground cayenne pepper
• Salt and black pepper to taste

Prepare all vegetables as described.

In a 4-quart saucepan over medium heat, add all the vegetables, milk, and spices. Cover and bring to a simmer. Don’t boil the mixture.

Once the celeriac is fork tender, remove from the heat and puree with an immersion blender, or a conventional blender. (Be careful not to burn yourself when pureeing hot food in a conventional blender.)

Slowly add the diced butter, grated Parmesan cheese, and lemon zest and continue blending until you have a smooth puree.

Add salt and black pepper until seasoned to taste.

Set aside for later use or cool uncovered in the fridge.

Gratin

Cook time: 2 hours (30 minutes active time)

• 4 to 6 Russet potatoes, peeled and soaked in water
• Celeriac puree (or puree of any root vegetable)
• 5 ounces Parmesan cheese, grated
• Kosher salt
• Butter
• Optional: Fresh thyme, to garnish

The goal here is to create layers of thinly sliced potatoes and celeriac puree until the pan is mostly full, and then cover with the grated Parmesan cheese.

Preheat your oven to 375 degrees.

Grease the bottom and sides of a 9-by-13 baking dish with butter.

Thinly (1/16th to 1/8th inch) slice the potatoes. (I use my mandolin for this and only slice one or two potatoes at a time to prevent the slices from browning.)

Place a layer of potatoes that slightly overlap each other (think fish scales or shingles) over the entire surface of the baking dish.

Sprinkle lightly with kosher salt and then spread a thin (1/8- to ¼-inch) layer of the celeriac puree on top.

Repeat these steps until the pan is mostly full. If you want, you can sprinkle some of the Parmesan cheese every couple layers for extra cheesy goodness.

Top the gratin with the rest of the Parmesan cheese and bake until the potatoes are fork tender and the top is golden brown.

Remove from the oven and let sit for 15 minutes before serving.

Pro tip: You can finish this with your broiler to get a crispier top if you like, just be careful not to burn it.

A version of this story originally published in the Sacramento Bee.

This story was originally published December 14, 2021 at 3:54 PM with the headline "Celeriac and Parmesan gratin is comfort food with a touch of fancy."