Put the flour with the butter in a planetary mixer and work them with the flat beater or k.
Meanwhile, dissolve the yeast and sugar in 100 g of warm milk.
Add the latter to the flour while continuing to knead.
Add the rest of the milk, and finally the salt while continuing to knead.
After 3 minutes, change the flat beater with the hooked one and knead the dough for at least 8 minutes, until it becomes smooth and soft.
Transfer the dough to a pastry board and form a ball.
Put it in a large bowl and cover it with cling film.
Let it rest until it rises double.
At this point divide the dough, form balls of about 65g (2.3 oz) each.
Arrange them on a baking tray, cover them, and let them rise for another hour.
As soon as they rise, flatten them with a rolling pin and on one half put a piece of mozzarella and a slice of ham.
Close them in with the other half, forming a half-moon, being careful to seal the edges well.
Fry in an abundance of oil and stop when they reach a golden brown on both sides.
Remove excess oil by transferring them onto absorbent paper.
Eat them hot.