To make the gnocchi, boil the potatoes in their skins until cooked, drain, allow to cool slightly, then remove the skins and mash.
Combine with the flour, egg, a little salt to taste, and half of the lemon zest.
Mix until you obtain a soft dough. Sprinkle a little rice flour over a work surface and roll out the dough into long sausage shapes.
Using a sharp knife, cut into roughly 3/4-inch (2 centimeter) lengths. Set aside.
Bring a large pot of lightly salted water to a boil.
Drop the gnocchi into the water, in batches, and simmer for a minute or so until they rise to the top.
Meanwhile, put the butter in a large frying pan with the mint leaves and lemon juice and melt over medium to low heat.
Remove the gnocchi with a slotted spoon and add it to the butter sauce with a little of the cooking water.
Cook for a minute or so until all the gnocchi are coated in the sauce, add the Parmesan, mix well, and serve immediately with extra Parmesan and the remaining lemon zest.