Directions

Cook the penne according to package directions until al dente. Drain and set aside to cool.

Heat oven to 375°F. Bake potatoes until tender, about 45 minutes. Let them cool slightly, then peel the potatoes with your hands. The peels should come off easily. Discard the skins. Push the potatoes through a ricer into a medium-sized bowl. Stir in the butter, truffle oil and scallions until well mixed. Season with salt and pepper. Using your fingers, press the potato mixture evenly across the bottom of a 9-inch springform pan. Bake until lightly browned on the edges, about 25 minutes. Let cool on a wire rack.

Bring the half-and-half to a boil in a medium-sized saucepan set over medium heat, stirring occasionally. Remove from heat and stir in the red pepper flakes. Let the mixture cool slightly, then briskly whisk in eggs, egg yolks, Asiago, and nutmeg. Season with more salt and pepper and set aside.

Heat vegetable oil in a large skillet set over medium heat. Add shallots and cook, stirring occasionally, until softened, about 2 minutes. Add the kale and cook, stirring occasionally, until wilted, about 5 minutes. Remove from heat, season with salt and pepper and set aside.

Stir the cooked penne, Asiago mixture, kale mixture, prosciutto, and sage into a large bowl until well combined. Scrape this mixture over the potato crust and spread evenly. Top with the Parmesan cheese and bake until well-browned on the tips of the penne, about 45 minutes. Remove from oven and let cool slightly on a rack before releasing the springform pan. Slice into wedges and serve warm with additional Parmesan passed at the table.