1. Preheat oven to 350°F. Prick potatoes all over with fork, and bake 45 minutes to 1 hour, or until soft to touch. Slice open, and let cool 10 minutes.
2. Scoop out potato flesh (it will still be hot); reserve skins for another use. Mash potato flesh in bowl or put through potato ricer. Stir in salt, then egg with fork. Stir in potato starch until dough comes together and no longer sticks to fork or your hands.
3. Scoop out 1/2 cup dough, and roll into 3/4-inch-thick rope on work surface dusted with potato starch. Cut rope into 3/4-inch pieces. Set back of fork atop 1 gnocchi, and use fork to roll gnocchi toward you, making light indentations with fork tines. Transfer to parchment-lined baking sheet.
4. Bring pot of salted water to a boil. Add gnocchi, and cook 2 minutes, or until gnocchi float to top. Drain, and serve.
