Put peeled and cooked potatoes through ricer to measure three cups. Turn out on floured board and when cool enough to handle work in 1 cup sifted flour, 2 egg yolks and 1/4 cup grated Parmesan cheese. Use your hands and when blended roll out into ropes about as thick as your thumb. Cut into 1 inch lengths and press with the floured tines of a fork the long way so rolls are about half as thick. Drop carefully into large pot of boiling salted water. Boil until they float to the top, then remove with slotted spoon. Put on a hot platter and just before serving spoon over a little melted butter and grated Parmesan cheese, or any good spaghetti sauce may be used.