Rice peeled potatoes using a potato ricer into a large bowl. Add the whisked egg, salt, and flour. Mix by hand until well combined. Lightly flour a cutting board and continue kneading dough for an additional 20-30 seconds.
Roll the dough into a rope no thicker than 1/2". Cut the rope into 1/2" sections. Roll squares on the tines of a fork for gnocchi ridges. Bring another pot to a boil and add 15-20 gnocchi at a time. Boil until they begin to float. Remove from pot. Serve immediately with pesto or toss in a Lemon Garlic Sage Sauce.