Why It Works
- The wide surface area of a sheet pan exposes more of the gratin to direct oven heat, ensuring maximum browning and a higher crust-to-cream ratio, so every serving delivers both a crisp, cheesy top and a tender, saucy interior.
- Baking in stages—first covered and then uncovered—ensures the potatoes become tender, the sauce thickens, and the surface of the gratin becomes golden and crispy.
Once the fake-summer tease that is September finally passes and the air starts to smell faintly like wet leaves and sweaters, I, like many people, switch from salad mode to roasted root vegetable mode—preferably the kind that’s blanketed in cream and cheese. This sheet-pan root vegetable gratin is the dish I want to live on from the first cool day of fall straight through Thanksgiving. It’s a stunner: bubbling, golden, and layered with flavors that taste like the season itself.
This gratin, developed by our colleague Marianne Williams in the Birmingham, Alabama, test kitchen, proves that with the right mix of vegetables, cream, and cheese, along with good use surface area, a simple sheet pan can yield a perfectly browned, evenly cooked result. Instead of baking in a deep casserole dish, which is traditional for gratins, the vegetables are spread out across a rimmed baking sheet. That wider shape means more of the top layer turns brown and crisp, while the vegetables underneath melt into creamy submission. Every serving includes the best of both worlds—the browned, cheesy crust and the silky interior—without having to fight your neighbor for an edge piece. It’s also perfect for a crowd or the holiday table since one sheet pan easily serves 8 to 12.
Serious Eats / Photographer: Robby Lozano, Food Stylist: Jennifer Wendorf, Prop Styling: Abby Armstrong
The mix of root vegetables here isn’t random. Sweet potatoes bring earthy sweetness; parsnips add a little spice and bite; and golden beets lend both color and a faint minerality. It’s just the right combination of sweet, savory, nutty, and just a touch of peppery bite. The onions form the aromatic backbone, cooked gently in butter until soft and golden before being hit with a splash of dry sherry. That quick deglaze adds an acidic punch that keeps the gratin from tasting heavy, even though it’s unapologetically rich. The cream soaks up all that flavor, carrying it through every layer of the vegetable.
For cheese, Marianne found that Gruyère and Parmigiano-Reggiano are the winning duo. Gruyère melts into silky strings, while Parm adds sharpness for an extra-savory crust. Fresh thyme and sage thread welcome woodsy flavor through the dish without overpowering it—their aroma is the first to hit you as soon you open the oven door.
Serious Eats / Photographer: Robby Lozano, Food Stylist: Jennifer Wendorf, Prop Styling: Abby Armstrong
What comes out of the oven is something that looks like fall foliage smothered in cheese. It’s orange, gold, and pale cream, edged with crisp brown bits and bubbling corners. It’s hearty enough to anchor a vegetarian dinner, fancy enough for Thanksgiving, but low-stress enough for a weeknight if you plan ahead. Slice it into neat rectangles or let it rustically spill onto the plate—I guarantee it’ll be demolished either way.
This recipe was developed by Marianne Williams; The headnote was written by Leah Colins.
This Sheet-Pan Gratin Bakes Up Crisp at the Edges, Creamy in the Middle, and Totally Irresistible
Cook Mode
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3 tablespoons (42 g) unsalted butter, softened and divided
1 small yellow onion (4 ounces; 113 g), thinly sliced (about 1 cup)
3 teaspoons (9 g) Diamond Crystal kosher salt, divided; for table salt, use half as much by volume or the same weight
4 large cloves garlic, minced
1/4 cup (60 ml) dry sherry
2 cups (480 ml) heavy whipping cream
1 teaspoon chopped fresh thyme leaves, plus whole leaves for garnish
1 teaspoon chopped fresh sage, plus small leaves for garnish
1/2 teaspoon freshly ground black pepper, plus more for garnish
1/8 teaspoon freshly grated nutmeg
3 medium parsnips (5 ounces/141 g each), peeled
2 large sweet potatoes (12 ounces/340 g each), peeled
2 large trimmed golden beets (10 ounces / 283 g each), peeled
6 ounces (170 g) Parmigiano-Reggiano cheese, grated (about 1 1/3 cups), divided
6 ounces (170 g) cave-aged Gruyère cheese, shredded (about 1 1/2 cups)
Adjust oven rack to middle position and preheat oven to 450°F (230°C). Grease bottom and sides of a 17 1/2-by-12 1/2-inch rimmed baking sheet with 1 tablespoon of the butter. In a large skillet, melt remaining 2 tablespoons butter over medium heat. Add onion and 1/2 teaspoon salt and cook, stirring occasionally, until onion is softened and starts to turn golden brown, about 10 minutes. Add garlic and cook, stirring constantly, until fragrant, about 1 minute. Add sherry and cook, stirring constantly, until evaporated, about 1 minute. Reduce heat to low, and add cream, thyme, sage, pepper, nutmeg, and 1/2 kosher teaspoon salt; bring to a simmer over low heat, then immediately remove from heat.
Serious Eats / Photographer: Robby Lozano, Food Stylist: Jennifer Wendorf, Prop Styling: Abby Armstrong
While cream mixture sits, thinly slice parsnips, sweet potatoes, and beets on a mandoline into 1/8-inch-thick rounds. Arrange half of the vegetable slices in an attractive pattern on prepared baking sheet so that bottom of sheet is not showing, tightly shingling or overlapping as needed. Sprinkle evenly with 1 teaspoon kosher salt and 2/3 cup Parmigiano-Reggiano. Top with half of remaining vegetable slices, tightly shingling or overlapping as needed, and sprinkle with remaining 1 teaspoon kosher salt. Using a ladle, pour warm cream mixture evenly over vegetables.
Serious Eats / Photographer: Robby Lozano, Food Stylist: Jennifer Wendorf, Prop Styling: Abby Armstrong
Cover baking sheet tightly with aluminum foil; bake until vegetable slices are just tender when pierced with a fork, 20 to 30 minutes. Carefully remove foil, and sprinkle evenly with Gruyère and remaining 2/3 cup Parmigiano-Reggiano.
Serious Eats / Photographer: Robby Lozano, Food Stylist: Jennifer Wendorf, Prop Styling: Abby Armstrong
Return uncovered baking sheet to oven; bake at 450°F,until browned and crusty on top, rotating baking sheet halfway through, about 20 minutes total.
Serious Eats / Photographer: Robby Lozano, Food Stylist: Jennifer Wendorf, Prop Styling: Abby Armstrong
Remove from oven, and let sit for 5 minutes. Sprinkle with additional thyme leaves, sage leaves, and black pepper. Serve immediately.
Serious Eats / Photographer: Robby Lozano, Food Stylist: Jennifer Wendorf, Prop Styling: Abby Armstrong
Special Equipment
17 1/2-by12 1/2-inch rimmed baking sheet, mandoline, large skillet
Make-Ahead and Storage
The finished gratin and leftovers can be refrigerated in an airtight container for up to 4 days. Reheat in the microwave or in an oven-proof dish at 400ºF (205ºC) until heated through, about 10 minutes. (If making ahead, wait to garnish with fresh herbs until before serving.
