Cover potatoes in a large pot with cold water. Bring the water to a boil until the potatoes are easily pierced with a skewer (30 minutes) do not over cook. Drain potatoes and let stand until cool enough to handle. Scrape the skin off the potatoes with a paring knife. Press the peeled potato through a ricer. Spread the riced potatoes into a thin even layer on a work surface. Let cool completely.
In a small bowl, beat the egg, salt, pepper, and nutmeg together. Gather the cold potatoes into a mound and form a well in the center. Pour the egg mixture into the well. Knead the potato and egg mixture together with both hands, gradually adding the grated cheese and enough flour, about 1 1/2 cups, to form a smooth but slightly sticky dough. It should take no longer than 3 minutes to work the flour. Use a knife or dough scraper to scrape the sticky dough from the work surface back into the dough as you knead.
Wash and dry hands. Dust the dough, your hands and work surface lightly with remaining flour. Cut the dough into 6 pieces and set off to 1 side of the work surface. With 1 piece of dough, form a long rope using your hands in a back and forth motion.
Slice the rope into 1/2-inch pieces. Press each piece into the tip of a fork, with your thumb roll the gnocchi off the fork. Set on a baking sheet with flour.
Cook immediately in boiling salted water. They are cooked when they rise to the surface, about 1 minute. Toss in Creamy Lemon Sauce and serve.
Creamy Lemon Sauce:
Saute the minced garlic in butter on medium heat. Add the flour. Cook for 1 minute. Add the cream and lemon zest. After the gnocchi are cooked, toss in the sauce then top with Parmesan.