Ingredients
1 3/4 pounds russet potatoes (3 to 4 medium)
2 tablespoons unsalted butter, softened
2 scallions, white and light-green parts, finely chopped
Coarse salt and freshly ground pepper
1 cup whole milk
1 cup heavy cream
1 dried small red chile, crumbled
4 large eggs
4 large egg yolks
1/4 cup sour cream
1 1/2 cups Parmesan cheese, grated
1/4 teaspoon freshly grated nutmeg
2 tablespoons extra-virgin olive oil
1 shallot, finely chopped
1/2 large bunch (14 ounces) Swiss chard, stemmed and coarsely chopped
3/4 pound penne, cooked according to package instructions
1/4 pound prosciutto, thinly sliced into 1/4-inch strips
3 tablespoons fresh oregano, coarsely chopped
Preparation
Preheat oven to 375 degrees. Bake potatoes on a rimmed baking sheet until tender, about 45 minutes. Let cool slightly. Peel potatoes; discard skin. Mash with a potato masher. Stir potatoes, butter, and scallions in a medium bowl; season with salt and pepper. Press potato mixture evenly into bottom of a 9-inch springform pan. Bake until light golden, 25 to 30 minutes. Let cool on a wire rack.
Bring milk and cream to a boil in a medium saucepan over medium-high heat, stirring occasionally. Remove from heat; stir in chile. Whisk in eggs, egg yolks, sour cream, Parmesan, and nutmeg. Season with salt and pepper; set aside.
Heat oil in a large skillet over medium heat. Add shallot; cook, stirring occasionally, until light golden, about 2 minutes. Add chard; cook, stirring occasionally, until wilted, 3 to 4 minutes. Season with salt and pepper.
Stir pasta, Parmesan mixture, chard mixture, prosciutto, and oregano in a large bowl. Spread over crust. Bake until golden brown and set, about 45 minutes. Let cool slightly before serving.
