Root Vegetable Gratin For a Rainy Weekend

Root Vegetable Gratin with Mustard Cream

Thanksgiving has come and gone, its passing has left Los Angeles the gift of rain. So I’m going to make something warm and cozy. Something my mother might make. Maybe we’ll spend this first rainy evening having dinner in front of the fire. We have four leather chairs that pull around a table by the fireplace in a sort of a gentlemen’s club arrangement. Dining there suits the mood that prevails in this old house when the weather turns gray. It’s easy for my warm and cozy thoughts to turn to a gratin – a root vegetable gratin with sweet potato, celery root, and rutabaga.

My mother would call these thinly sliced vegetables “scalloped” but she and I would be thinking the same thing.

I’m not planning to scour the web looking for just the right root vegetable gratin. Nope, this time I want something warm and familiar. So I’ve adapted my standard “scalloped” potato gratin with Emmental cheese, cream and of course mustard (two ways). A little grainy mustard in the cream sauce and some whole mustard seeds sprinkled over the top for a nutty burst of heat in the crusty bits. Yummy!

Root Vegetable Gratin

The key to this Root Vegetable Gratin with Mustard Cream (or really any gratin including my mother’s scalloped potatoes) is in having all the vegetables sliced the same thickness so they cook at the same rate. Make friends with a mandoline: It quickly yields precise, even slices. I also like to blanch the vegetables in a milky solution. They bake creamier that way and much more evenly. If you’ll read the recipe you’ll see that the mandoline and the blanching are not the only shortcuts I take with this classic recipe. In this version, I skip the laborious béchamel and simply layer the root vegetables with grated cheese and a sprinkle of flour. Then when I pour the mustard-cream sauce over the top the béchamel makes itself while baking.

That’s it! Serve it while it’s hot and bring on the rain! “Just don’t track muddy footprints all over the house” (that was my mother speaking)… GREG

Root Vegetable Gratin with Mustard CreamRoot Vegetable Gratin with Mustard Cream

Root Vegetable Gratin with Mustard Cream 

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Root Vegetable Gratin with Mustard Cream


  • unsalted butter (as needed for baking dish)
  • 2 teaspoon whole yellow mustard seeds (divided)
  • 2 pound assorted root vegetables (such as sweet potatoes, celery root, and rutabega) (peeled and very thinly sliced)
  • 2 clove peeled, whole garlic
  • 2 cup whole milk
  • 2 cup water
  • 1 cup cream
  • 1 tablespoon Dijon mustard
  • kosher salt (to taste)
  • ground white pepper (to taste)
  • 2 tablespoon all-purpose flour
  • 6 ounce grated Emmental cheese (or similar)


Preheat oven to 375 degrees F.

Butter the sides and bottom of a 10″ x 7″ inch oval baking dish. 

Using a mortar and pestle, grind 1 teaspoon of the mustard seeds into a very coarse powder. Set aside. 

In a large saucepan, combine sliced root vegetables, garlic, milk, and water. Bring the mixture to a boil, then reduce the heat to medium-low. Simmer about 5 minutes until the vegetables begin to soften; drain, saving 1‑cup of cooking liquid. Discard garlic; set vegetables aside.

Combine the reserved cooking liquid with the cream. Whisk in the Dijon mustard and the roughly ground mustard seeds. Season with salt and white pepper. 

Layer the softened vegetables in the baking dish, sprinkling a little flour and some of the cheese between each layer. Reserve half of the cheese for the top. Slowly pour the mustard-cream mixture over the vegetables until it comes almost to the top of the dish. Sprinkle with the remaining cheese and distribute the remaining whole mustard seeds evenly across the top. Place the baking dish on a cookie sheet to catch the bubble over. Bake in the heated oven for 25 to 30 minutes, or until browned and bubbly. Let the gratin rest about 5 minutes before serving.