In a large mixing bowl, add all the ingredients except for the oil.
beat with a fork until a ball starts to form, a few minutes.
Transfer the dough to a wooden board, add a touch more flour if dough is moist.
Knead with your hands until dough is smooth, a few minutes.
Wrap in saran wrap and let rest at room temperature for half hour.
Remove a piece of dough from the ball (about ¼), and roll into a log.
Cut the log into pieces, and roll each piece into one ball. Each ball should weigh about 20 grams. Repeat this process until all the dough is formed into balls.
Heat the oil in a small saucepan. Once hot enough to fry (I always test with a wooden spoon- insert the end of the spoon into the oil - if it starts to bubble, it's ready), drop about 4-5 balls in the oil.
Fry the ball until they are golden in color - about 2 minutes. If they are frying to fast, reduce the heat of the oil.
Remove using a skimmer and place the castagnole on a plate lined with paper towel.
Repeat this process for all the balls.
While the castagnole are frying, place granulated sugar in a small bowl and roll the castagnole in the sugar to coat them.
Fill a pastry bag attached with a piping tip with the pistachio cream.
Pierce each castagnola with a straw, without it coming through the other end.
Insert the piping tip into the open end of the castagnola and squeeze the pistachio cream in. Repeat with all castagnole.
Serve and enjoy!