"Gnudi (or'naked' ravioli without a pasta jacket) are tender dumplings simmered like gnocchi and, when made with sweet potatoes and finished in sage butter, present beautifully for a delicious autumn dish."
When cool enough to handle, cut potatoes in half, scoop out the cooked potato. Mash the potato on a large place to cool and release some moisture. Let sit for at least 30 minutes.
Mix potato with egg yolks, ricotta cheese, grated cheese, salt, pepper, and nutmeg.
Add the flour a little at a time until the dough just starts holding together. Scoop out teaspoons of dough and roll into small, marble-sized balls (they will expand when cooked). Place on lightly floured surface so they don't stick together. Refrigerate for 1 hour or, ideally, overnight.
Bring a large pot of salted water to a boil, then turn heat down so water continues to simmer. Add gnudi, about a dozen at a time, and simmer until they rise to the surface, about 4 minutes; continue simmering for another 4 minutes. Remove from the water with a slotted spoon and place in a bowl. Keep them warm as you cook the remaining gnudi.
Melt the butter in a large skillet over medium heat. Add the whole sage leaves until they are wilted and beginning to brown; remove from skillet and set aside. Add the chopped sage and cook until butter begins to brown. Add the gnudi and cook until gnudi are coated with butter and sage. Garnish with the whole sage leaves.
Top with more grated cheese; you can serve these from the skillet or plate separately.