These little elongated pear-shaped cheese are made of cows' milk and moulded around a pat of butter (burro), from whence their name; in fact they were invented in the days before refrigeration as a method of preserving butter from going rancid in warm climes. They are left to ripen for several weeks, and usually eaten on bread. Outside of Italy, you will often find them dipped in wax to give them a longer shelf life.
Sometimes called butirro or burielli.
In Rionero in Vulture, in the Basilicata they make a particularly interesting version called burrino farcito: within the butter is a ball of sausage soppressata.
Images by: tuscantraveler