Boil the potatoes in salted water.
Leave to cool but not completely and knead with the two flours.
Form a compact dough.
In the meantime prepare the 3 fillings, cut them into small pieces.
Form your cylinders, then cut into cubes.
With your finger form a small hole and place inside: a piece of mozzarella in one, another a piece of stracciatella, another still a piece of blue cheese.
Close well and form small balls.
Pass them in the flour if they are too dry and they are likely to open, move them on a floured tray.