In a bowl, mix the ricotta, Parmigiano cheese, flour, nutmeg, egg yolks, and salt and pepper. Knead the mixture until it becomes a doughy consistency. If the mixture appears to be too moist, add a bit more flour, as needed. Cover the dough with a cloth and let it rest for half an hour. Grab a handful of dough at a time and roll it into 1-inch thick logs. Cut each log into 1-inch pieces. Roll each piece of dough against a cheese grater to create ridges. These ridges will help trap the sauce on each cooked dunderi. Dust a baking tray with flour and place the dunderi on top so they won't stick together. In a pot of boiling salted water, cook the dunderi for 5 minutes, or until they float to the top. Mix with your choice of sauce, and serve immediately.