Vegetable Gratin with Blue Cheese Sauce

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.

Thanksgiving Root Vegetable Gratin topped with chopped nuts and served in a casserole dish.
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.

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.
Sarah Fritsche

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.
Sarah Fritsche

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.

More of Our Favorite Holiday Sides

Vegetable Gratin with Blue Cheese Sauce

Prep Time 40 mins
Bake 45 mins
Total Time 85 mins
Servings 6 to 8 servings


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 shallots, thinly sliced

  • 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 (34g) 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 pecans, chopped


  1. Preheat the oven, prepare the baking dish

    Preheat the oven to 375°F.

  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.
    Sarah Fritsche
  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
    Sarah Fritsche
  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.
    Sarah Fritsche
    How to Make Root Vegetable Gratin by making a cheese sauce in a dutch oven.
    Sarah Fritsche
  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.
    Sarah Fritsche
  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.

Nutrition Facts (per serving)
442 Calories
33g Fat
32g Carbs
9g Protein
Show Full Nutrition Label Hide Full Nutrition Label
Nutrition Facts
Servings: 6 to 8
Amount per serving
Calories 442
% Daily Value*
Total Fat 33g 42%
Saturated Fat 15g 77%
Cholesterol 67mg 22%
Sodium 611mg 27%
Total Carbohydrate 32g 12%
Dietary Fiber 7g 27%
Total Sugars 12g
Protein 9g
Vitamin C 18mg 90%
Calcium 225mg 17%
Iron 2mg 9%
Potassium 798mg 17%
*The % Daily Value (DV) tells you how much a nutrient in a food serving contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.
Nutrition information is calculated using an ingredient database and should be considered an estimate. In cases where multiple ingredient alternatives are given, the first listed is calculated for nutrition. Garnishes and optional ingredients are not included.