- ¾ cup cream
- ¾ cup milk
- ½ cup pumpkin purée
- 3 garlic cloves, smashed
- 2 sprigs fresh thyme, more for garnish
- ¼ teaspoon freshly ground nutmeg
- 4 ounces shredded melting cheese (like an Italian Fontina, Havarti or Swiss cheese, shredded)
- ½ cup grated aged cheese (like Parmigiano Reggiano or Hickory Nut Farm’s Chebar)
- Butter, softened, to grease the pan
- 2 pounds waxy yellow potatoes, peeled and cut into ⅛-inch slices
- 2 pounds sweet potatoes, peeled and cut into ⅛-inch slices
- Kosher salt and freshly ground black pepper
- Thyme leaves, for garnish
In a medium saucepan, combine cream, milk, pumpkin, garlic, thyme and nutmeg, and place over medium-low heat. Bring the mixture to a simmer and then remove it from the heat. Let the thyme steep in the mixture for 30 minutes and then remove them from the pot.
Preheat the oven to 375°. Combine cheeses in a medium bowl and set aside.
Butter the inside of a baking dish large enough to hold the potatoes snugly. Arrange the potato slices––alternating between waxy and sweet potatoes and slightly overlapping each––in 3 rows on the bottom of the baking dish. Sprinkle potatoes with salt and pepper. Spoon 1/3 of the cream sauce over the potatoes. Sprinkle with 1/3 of the cheese mixture. Repeat this layer process twice more, leaving the cheese off the top layer. Bake, covered tightly with aluminum foil, for 30 minutes. Remove foil and bake for 15 minutes more. Sprinkle the last of the cheese on top and bake for 5-10 more minutes until the cheese melts and begins to brown. Let casserole rest for 15 minutes. Serve with a sprinkling of fresh thyme leaves.