The world's most expensive cheese is called pule, which comes from a Balkan donkey. It can cost $600 per pound due to the fact that donkey milk is hard to produce and very rare.

A cow can produce anywhere from about 22 liters up to 60 liters of milk a day, but a female donkey (called a jenny) only produces about 1.5-2 liters of milk per day.

The domesticated Balkan donkeys that are milked for pule live on a nature reserve in Serbia called Zasavica, and according to the BBC, there are about 180 of them.

If you want their milk, you must milk them by hand, three times a day, because no machinery currently exists for the large-scale milking of donkeys.

Pule is made of 60% donkey milk and 40% goat milk and is aged for a month, made in pretty much the same way as goat cheese with a few extra production secrets.