The cognac in a Vieux Carre' lightens and softens the rye, but the armagnac in the Old Square also adds a layer of its own flavor and richness, especially if your bottle has been sitting around as long as mine has (Dartigalongue Hors d'Age, opened some time back in the late 20th century). Replacing some of the rosso in a Vieux Carre' by oloroso sherry adds another layer of complexity and richness as well without making it sweeter; the sweetness is about right as specified here. An excellent Vieux Carre' variant.