Vegetable Gratin with Blue Cheese Sauce

Side DishThanksgivingBlue CheeseGratinRoot Vegetables

Parsnips, carrots, and fennel are thinly sliced, then dressed in a decadent cream sauce infused with sweet and earthy blue cheese. Topped with chopped pecans and baked until golden and bubbly, this is your elegant holiday side dish.

Photography Credit: Sarah Fritsche

At its heart, a gratin is simply some sort of filling, often vegetables (root or otherwise) loaded with cheese, butter, and topped with breadcrumbs, then baked in a shallow baking dish or gratin. It’s about as homey and comforting as you can get.

Seriously, butter, cheese, cream. What’s not to love? Baked until golden brown and bubbly, this makes a lovely side dish for prime rib, ham, or other holiday roast.

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NOT TRADITIONAL BUT UTTERLY DELICIOUS

I break from tradition a bit with this gratin, but the flavors work together beautifully. If you’re craving something new, interesting and delicious this is the recipe for you!

Potatoes are probably the most familiar vegetable used in gratins, but for this, I lean into the root veggie’s sweet and earthy cousins: carrots and parsnips.

A bit of fennel, with its delicate licorice notes, is also added to the mix. For the topping, chopped pecans replace commonly used breadcrumbs.

The cheese sauce in this recipe is a béchamel enriched with sweet and earthy blue cheese, which technically makes it a Mornay sauce, but I’m a fan of alliteration, so blue cheese béchamel, it is.

HOW TO MAKE SMOOTH BÉCHAMEL

  • Keep your béchamel lump free and silky smooth by warming up the milk and cream together in a separate pan, then slowly whisking the liquid into the butter and flour (a.k.a. roux) a little bit at a time so the flour and butter mixture can better absorb the liquid.
  • Cooking the sauce over a steady medium to medium-low heat, along with stirring frequently, will help to prevent the béchamel from scorching.

Vegetable Gratin with Parsnips, Carrots, Fennel and Blue Cheese set in the middle of a white plate with the rest of the casserole set behind it.

WHEN IT COMES TO VEGETABLES: THINK THIN

  • A mandoline helps make quick work of the carrots and parsnips, giving you perfectly even and thin (about 1/8-inch) slices with every stroke. (Just be sure to watch your fingers and knuckles as you work!)
  • However, if you don’t have a mandoline, don’t fret; a very sharp chef’s knife and a little patience will also do the trick.

SWAPS AND SUBSTITUTIONS

  • Don’t like blue cheese? Whisk in some grated Parmesan or Pecorino Romano instead. A smoked gouda could also be fun.
  • You could even swap out the parsnips and carrots for different root vegetables; a combination of celery root and potatoes would be especially nice.

Thanksgiving Root Vegetable Gratin piled in the center of a white plate with a fork to the left.

MAKE AHEAD

  • I don’t recommend freezing the gratin, but to save time, you can assemble it unbaked the day before you plan to serve it. When you’re ready to bake, remove the gratin from the refrigerator, and let it sit for about 30 minutes to come to room temperature before popping in the oven.

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Vegetable Gratin with Blue Cheese Sauce Recipe

  • Prep time: 40 minutes
  • Bake time: 45 minutes
  • Yield: 6 to 8

Ingredients

For the gratin:

  • 1 1/2 pounds parsnips, scrubbed and peeled
  • 1 pound carrots
  • 1 fennel bulb (about 8 ounces), trimmed
  • 2 tablespoons unsalted butter, plus more for greasing
  • 1/2 cup thinly sliced shallots
  • 1/2 teaspoon salt, plus more as needed
  • 1/4 teaspoon freshly ground black pepper, plus more as needed
  • 1 clove garlic, minced
  • 2 teaspoons fresh thyme leaves, finely chopped

For the béchamel, and to finish:

  • 2 cups whole milk
  • 1 cup heavy cream
  • 3 tablespoons unsalted butter
  • 3 tablespoons (34 grams) all-purpose flour
  • 3 ounces blue cheese, crumbled
  • 1 teaspoon salt
  • 1/2 teaspoon freshly ground black pepper
  • 1/8 teaspoon freshly grated nutmeg
  • Pinch ground cayenne pepper, optional
  • 1 cup chopped pecans

Method

1 Preheat the oven, prepare the baking dish: Preheat the oven to 375℉.

2 Slice the vegetables: Using a mandoline or a very sharp chef’s knife, cut the parsnips and carrots diagonally into slices about 1/8-inch thick. Halve the fennel, then cut into slices about 1/8-inch thick.

Fennel, carrots and parsnip sliced and set in piles on a table to make Root Vegetable Gratin with Blue Cheese Béchamel.

3 Sauté the aromatics and fennel: Melt the butter in a sauté pan over medium-high heat. When the butter is foamy, add the shallots, and cook until soft and translucent, about 3 minutes. Add the fennel, and cook until just tender, 4 minutes. Season with 1/2 teaspoon salt and 1/4 teaspoon pepper. Stir in the garlic and thyme, and cook until aromatic, another 30 seconds.

A dutch oven with melted butter inside to make a Vegetable Gratin with Parsnips, Carrots, Fennel and Blue Cheese

4 Layer the vegetables: Grease a large (2 quart) gratin dish or a 9-x-13-inch glass baking dish with butter. Layer half of the parsnips in the gratin dish, sprinkle with a pinch of salt and a grind of black pepper.

Top with half of the carrots, and season with another pinch of salt and grind of black pepper. Scatter half of the fennel mixture on top of the carrots.

Repeat with the rest of the parsnips and carrots, finishing with the remaining fennel mixture. Set aside.

5 Begin the béchamel: You'll need two sauce pans, one small and one medium.

In a small sauce pan set over medium-low heat, add the milk and cream.

In a medium saucepan set over medium heat, add the butter. When the butter foams, whisk the flour into the melted butter, and cook until nutty smelling and light golden in color, about 3 minutes.

6 Add the milk to the roux: Slowly whisk the warm milk and cream a little bit at a time into the butter and flour mixture (roux) until combined. The sauce should be smooth.

Bring the béchamel to a simmer, keeping an eye on the heat and stirring frequently to prevent scorching. It will really start to thicken as it simmers.

Reduce the heat to medium-low, and simmer until the sauce is thick and coats the back of a spoon, about 4 minutes.

Sauce for Thanksgiving Root Vegetable Gratin in a pot with a whisk inside. How to Make Root Vegetable Gratin by making a cheese sauce in a dutch oven.

7 Remove from heat and add the cheese: Remove the béchamel from the heat and whisk in the blue cheese a few crumbles at a time. Season the sauce with salt, pepper, nutmeg, and a pinch of cayenne, if you want a little heat. Taste and adjust the seasoning, if desired.

8 Add the béchamel to the vegetables: Pour the warm béchamel over the top of the vegetables in the gratin dish and let sit for at least 15 minutes to allow the sauce to soak into the vegetables.

Scatter the pecans over the top of the gratin. (The gratin can be made ahead up to this point, then refrigerated until ready to bake.)

A casserole dish with Cheesy Root Vegetable Gratin with Parsnips, Carrots and Fennel unbaked inside.

9 Cover and bake: Snugly cover the gratin with foil and bake for 45 minutes. Uncover and bake for another 20 minutes, or until the gratin is golden brown and bubbly, and the vegetables are tender when pierced with a knife.

10 Serve: Let rest 20 minutes before serving.

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Sarah Fritsche

Sarah Fritsche is a San Francisco-based food writer and recipe developer. For over adecade she was a staff writer with ​The San Francisco Chronicle​’s James BeardAward-winning Food team, where she reported on the Bay Area’s food scene,interviewed culinary luminaries, including Nigella Lawson, Dorie Greenspan, andJacques Pépin, and headed up ​The Chronicle​’s test kitchen.

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A baked Vegetable Gratin with Parsnips, Carrots, Fennel and Blue Cheese topped with chopped nuts served in a casserole dish.Vegetable Gratin with Blue Cheese Sauce