Edgar Allan Poe's "The Cask of Amontillado" is a story of revenge and madness. Montersor, the protagonist of the tale, lures Fortunato into the catacombs in order to bury him alive behind a wall for the "thousand injuries" inflicted upon him by Fortunato. Planning to draw Fortunato into the catacombs willingly, Montersor asks some advice of Fortunato.
It so happens that Montresor possesses a cask of Amontillado (a sherry which is alluded to to being rare, especially during carnival). Montresor openly questions the authenticity of the sherry, covertly challenging Fortunato with verifying it to be real. Knowing that Fortunato believes himself to be connoisseur, Montresor knows that he would desire the chance to authenticate the Amontillado. This is what Montersor plans on in order to get him into the recesses of the catacombs.
Essentially, Montersor asks Fortunato for his advice upon a cask (barrel) of Amontillado.