Ingredients

• 2 cups heavy cream
• 3 cloves garlic, smashed
• 1 bundle fresh thyme
• Pinch cayenne
• Kosher salt
• 1/2 stick butter, plus more for greasing
• 2 pounds turnips, peeled and very thinly sliced
• 1 1/2 cups grated Parmigiano-Reggiano
• 1 pound sweet potatoes, peeled and very thinly sliced

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Instructions

1. Special equipment: a mandolin; an 11-by-7-inch baking dish
2. Preheat the oven to 375 degrees F.
3. Place the cream, garlic, thyme and cayenne in a saucepan, and season with salt. Taste to make sure it is adequately seasoned. Bring to a boil and then turn off the heat. Steep the mixture for 15 to 20 minutes.
4. Grease the baking dish and layer in one-third of the sliced turnips. Sprinkle one-sixth of the grated cheese over the turnips and dot with one-sixth of the butter. Remove the thyme and garlic from the cream and pour one-sixth of the cream over the turnips. Repeat the layering five more times, alternating the turnip with sweet potato, until all of the ingredients are used up, for a total of six layers.
5. Cover the dish with foil, place on a baking sheet and bake for 35 to 40 minutes. Remove the foil and bake until golden, another 20 minutes. When done, a fork should slide in and out of the center of the dish easily.
6. Rest the dish 10 to 12 minutes, then serve.