
Spanish brandy is a grape-wine brandy from Spain, almost always Brandy de Jerez. It is aged by the solera system in sherry-seasoned casks around Jerez de la Frontera.
The closest one-for-one swap. Cognac runs a little drier, which hardly shows in a punch. In a short serve, a little syrup helps.
Sherry
Will not work. It is a wine, not a distilled spirit. The mix-up comes from Spanish brandy aging in old sherry casks.
In a solera, a portion is drawn from the bottom tier and replaced from above. A bottle therefore holds spirit of several ages rather than one year. An age on the label is an average, not a floor.