Boil, peel and mash the potatoes. Knead into a dough with the egg, flour and semolina. Season with a little salt.
Dust the work surface with flour and form the dough into rolls as thick as a thumb. Cut into 1 cm wide pieces. Put the pieces in boiling salted water and remove them as soon as they float on the surface of the water.
In the meantime, toss some sage in butter, add the cooked gnocchi to the pan immediately after cooking and fry a little. Serve immediately.
You can also serve the gnocchi with creme fraîche. Simply mix 1 cup of creme fraîche with salt, pepper, lime juice and chives.