Nairobi, Aug. 6 -- Not many invitations warrant clearing your calendar, but the chance to taste black truffles right here in Kenya is perhaps one that does.

These "diamonds of the kitchen," as they are sometimes called, are known to be among the world's rarest and most expensive ingredients, capable of elevating even the simplest dish. So when Mandhari restaurant at Nairobi Serena Hotel extended an invitation to experience them firsthand, I was more than happy to accept.

Our dinner party was small and intimate, but anticipation hung thick in the air until the restaurant's executive chef, Eshton Muthama, emerged carrying a plate on which rested a jet-black, knobbly sphere that was no bigger than a golf ball. It reminded me of a black-ski...