After completing the Dark Brotherhood quest 'To Kill an Empire', the player receives the Gourmet's Writ of Passage. If it is kept, an additional speech option appears when talking with Balbus: "I am the Gourmet!". Balbus will respond with praise and offer his fork. The fork can also simply be stolen, or taken from his corpse.
Balbus is difficult to locate, as he appears as a random encounter. A list of possible locations for Balbus can be found here.