Sweet Potato and Gruyère Gratin
This rich, cheese-laden gratin is a more savory take on the usual Thanksgiving sweet potato casserole, with sage and rosemary giving it an herbal bite. If you'd like to make it partway ahead, you can peel and slice the potatoes the day before; store in a sealable plastic bag in the fridge. You can also simmer the cream mixture (don’t add eggs) and grate the cheese the day before as well, storing them covered in the refrigerator.
- Serves: 12 persons
- 3tablespoons unsalted butter, softened, for pan and foil
- ⅓cup grated Parmesan
- 2cups heavy cream (or half-and-half)
- 3tablespoons fresh sage, chopped
- 1tablespoon fresh rosemary, finely chopped
- 3fat cloves garlic, grated or minced
- ¼teaspoon freshly grated nutmeg
- 1 ½teaspoons kosher salt, plus more as needed
- 3large eggs, lightly beaten
- 3pounds sweet potatoes (about 4 large or 5 medium), peeled
- Freshly ground black pepper, to taste
- 1 ⅔cups/6 1/2 ounces grated Gruyère
Step 1Heat oven to 400 degrees and generously butter a 9-by-13-inch baking pan or shallow gratin dish. Butter a piece of foil large enough to cover top of pan. Sprinkle Parmesan all over bottom of pan.
Step 2In a medium pot, bring cream, sage, rosemary, garlic, nutmeg and a pinch of salt to a simmer. Simmer until reduced by 1/4, about 10 minutes.
Step 3In a large, heatproof bowl, whisk eggs just enough to break them up. Slowly pour hot cream into eggs to combine, whisking while pouring, and reserve the mixture.
Step 4Meanwhile, using a mandoline or sharp knife, slice the potatoes into 1/8-inch-thick rounds.
Step 5Place 1 layer of potatoes in the pan, slightly overlapping as you go, using about a third of the slices. Sprinkle with 1/4 teaspoon salt and pepper to taste, then pour 1/3 of the egg mixture over potatoes. Top with 1/2 cup Gruyère. Repeat with another layer of potatoes, 1/2 teaspoon of salt, pepper and 1/3 egg mixture. Top with 1/2 cup Gruyère. Top with remaining potatoes, 1/4 teaspoon salt, pepper to taste, and remaining egg mixture (but not the remaining cheese). Press down to compact the potatoes. Cover with foil and bake until potatoes are tender, about 40 minutes, then remove foil, sprinkle top with remaining 2/3 cup Gruyère and bake until browned and bubbling, 25 to 30 minutes. Let cool slightly, then serve.