Sift the flour, potato starch and baking powder directly onto your work surface.
Make a well in the flour mixture and add the remaining ingredients, except for the frying oil and sugar for sprinkling.
Whisk the ingredients together with a fork, and once they are fairly well incorporated, begin kneading the dough.
Knead the dough until it’s smooth and elastic.
Form the dough into a ball, wrap in plastic wrap, and allow the dough to rest in the refrigerator for an hour.
Pinch off small pieces of dough (about 10 grams / 1/3 ounce eacand roll into small balls.
Each ball should be about 2 centimeters / 3/4 inch in diameter.
Heat the oil to 175°C before you begin frying the castagnole.
Make sure that the temperature doesn’t go above 175°C the whole time you are frying. Otherwise you run the risk that the castagnole will be too brown on the outside and raw on the inside.
Have enough oil in the frying pan so the castagnole are almost fully immersed.
Fry the castagnole for several minutes, until golden, turning frequently so they fry evenly.
Drain the castagnole on newspaper covered with paper towels.
Toss in sugar and serve!