Potato Gnocchi with Pesto
Peel the potatoes and press them through a ricer into the bowl of a heavy-duty electric mixer fitted with the paddle blade. (You can also rub the potatoes through a coarse wire sieve into a large bowl and use a sturdy hand mixer or spoon instead of the standing mixer.) Mix the egg and salt in a small bowl. With the machine on low speed, gradually mix in the egg, being careful not to do it too quickly or the egg will curdle. Gradually mix in enough flour to make a soft but malleable dough with a consistency similar to Play-Doh.
Dust a large baking sheet with flour. Turn the dough out onto a lightly floured work surface. Working with one-fourth of the dough at a time, roll the dough under your palms on the work surface to shape it into a long 1/2-inch-thick rope. Using a sharp knife, cut the rope into 1-inch-long pieces. Transfer the gnocchi to the floured baking sheet. Repeat with the remaining dough. (The gnocchi can be covered with plastic wrap and refrigerated for up to 2 hours before cooking. To freeze, cover the gnocchi with plastic wrap and freeze on the baking sheet just until frozen and firm, about 2 hours. Transfer the frozen gnocchi to self-sealing plastic freezer bags and freeze for up to 2 months. Do not thaw the gnocchi before cooking.)
Bring a large pot of lightly salted water to a boil over high heat. Fill a serving bowl with very hot water and let stand to warm the bowl. Toss the water out of the bowl and dry the bowl when the water in the pot comes to a boil.
Add about a dozen gnocchi to the boiling water and cook until 10 seconds or so after the gnocchi float to the top of the water. Using a wire skimmer or sieve, scoop the gnocchi out of the water, transfer to the warmed bowl, and cover to keep warm.
Add the pesto and about 1/3 cup of the cooking water. Stir gently to coat the gnocchi. Serve immediately and serve the Parmesan on the side.