Remove skins and force potatoes through the medium disk of a food mill into a bowl and beat in 3/4 to 1 cup of flour, 2 egg yolks and salt to taste. Transfer mixture to a lightly floured board and gently knead dough, adding additional flour, if necessary, to form a soft, smooth but slightly sticky dough. Do not overwork dough.
Divide dough into three equal parts. Working with one piece of dough at a time roll it into a rope about 1 inch in diameter and cut it into 3/4-inch pieces. Gnocchi may be transferred to a lightly floured baking sheet and chilled for 30 minutes. The gnocchi can be cooked as is or they can be shaped. To shape gnocchi: Using a fork with rounded long, slim tines, and holding it parallel to counter, concave side facing you, press a piece of dough against the inside curve of the fork just below the prongs using your index finger. Flip dough away from tip of fork in the direction of the fork's handle
In a large pot, bring 4 quarts water to a boil. Add salt to taste and enough gnocchi to cook without crowding the pan. Once gnocchi have floated to surface simmer for 10 to 15 seconds more, or until just firm. With a slotted spoon transfer gnocchi to a bowl. Cook remaining gnocchi in same manner. and keep warm.
Divide gnocchi among serving plates and nap with tomato sauce. Serve with freshly grated cheese.
Recommended Wine: 1994 Roero Arneis, Bruno Giacosa