WHY THIS RECIPE WORKS:
For a new twist on a classic potato gratin, we created a decidedly savory and elegant sweet potato version. To mitigate some of the potatoes’ natural sweetness, we turned to earthy, slightly bitter Swiss chard, which we sautéed in butter with shallot, garlic, and thyme. We shingled half the sliced potatoes along the bottom of the gratin dish, topped them with the chard, and then layered on the remaining potatoes.
Pouring a combination of water, wine, and cream over the vegetables encouraged the potatoes to cook evenly and imparted a welcome richness. Covering the gratin dish for the first half of baking ensured that the potatoes cooked through. We then uncovered the dish so that the excess liquid could evaporate and the cheesy topping could brown. Slicing the potatoes ⅛ inch thick is crucial for the success of this dish; use a mandoline, a V-slicer, or a food processor fitted with a ⅛-inch-thick slicing blade.
SERVE: 4 to 6
TOTAL TIME: 1 hour 45 minutes
INGREDIENTS:
- 2 tablespoons unsalted butter
- 2 shallots, minced
- Salt
- 2 pounds Swiss chard, stemmed and cut into ½-inch-wide strips
- 3 garlic cloves, minced
- 2 teaspoons minced fresh thyme
- ¾ teaspoon pepper
- ⅓ cup heavy cream
- ⅓ cup water
- ⅓ cup dry white wine
- 3 pounds sweet potatoes, peeled and sliced ⅛ inch thick
- 2 ounces Parmesan cheese, grated (1 cup)
INSTRUCTIONS:
- COOK THE CHARD MIXTURE
- Adjust oven rack to middle position and preheat oven to 350 degrees.
- Melt butter in a Dutch oven over medium-high heat.
- Add shallots and 1 teaspoon salt and cook until shallots are softened, about 2 minutes.
- Stir in chard and cook until wilted, about 2 minutes.
- Stir in garlic, thyme, and pepper and cook until fragrant, about 30 seconds; transfer to a bowl.
- PREPARE THE CREAM MIXTURE
- Add cream, water, wine, and 1 teaspoon salt to the now-empty pot and bring to a simmer over medium-high heat.
- Remove pot from heat and cover to keep warm.
- ASSEMBLE THE GRAIN
- Shingle half of the potatoes evenly into a 3-quart gratin dish (or 13 by 9-inch baking dish).
- Spread wilted chard mixture evenly over potatoes.
- Shingle remaining potatoes over the top.
- Pour cream mixture evenly over the top and sprinkle with Parmesan.
- BAKE THE GRAIN
- Cover the dish with aluminum foil and bake for 20 minutes.
- Uncover and continue to bake until the gratin is golden and feels tender when poked with a paring knife, 40 to 50 minutes.
- Let cool for 10 minutes before serving.
