2 1/2 pounds russet potatoes
6 large egg yolks, at room temperature
6 tablespoons unsalted butter (3/4 stick), cut into 8 pieces, at room temperature
1/4 cup heavy cream, at room temperature
1 teaspoon kosher salt, plus more as needed
1/4 teaspoon freshly ground black pepper
1/8 teaspoon freshly ground nutmeg
1/2 cup finely shredded Swiss cheese, grated on the small holes of a box grater (about 1 ounce)