DURING A RECENT stint living in central Serbia, I became obsessed with kajmak, which, if you can imagine, is like a lovechild between cream cheese and salty French butter. Made from the skimmed fat of cows’ milk and then mixed with salt, its consistency can vary from rather runny and milky (new) to more like clotted cream (old).

My mother-in-law and her sisters run some sort of kajmak mafia in their hometown of Kraljevo: There are frenzied meetings to discuss which of the sisters—or their one friend they also allow in on...