Create four small, thick beds of kosher salt on a baking sheet. Rinse and dry the potatoes, then arrange each potato on the salt. Bake until potatoes are tender, 45 to 55 minutes.
Cut the potatoes in half lengthwise and let cool for 2 minutes. Then scoop out the flesh with a spoon and immediately pass the potatoes through a ricer onto a work surface. Let cool completely.
Make a trough in the center of the potato mound and add the egg, nutmeg, white pepper and 2 teaspoons salt. Top with the flour and knead the dough until smooth but not elastic, about 4 minutes. Dust with flour if dough becomes too sticky. Do not overwork the dough.
Divide the dough into portions and roll each portion into a rope 1/2-inch thick. Cut each rope into 1/2-inch pieces.
Bring a large pot of salted water to a boil.
Roll each dough piece on a floured fork and place on a floured baking sheet. In batches, add handfuls of gnocchi to the boiling water and cook until they float to the top, about 2 minutes. Remove with a slotted spoon and transfer to a sauce.