
Spanish brandy is a grape-wine brandy from Spain, almost always Brandy de Jerez, aged by the solera system in sherry-seasoned casks around Jerez de la Frontera.
Grape brandy aged in a sherry cask, so it is rounder and sweeter than the French style at the same age. A drier bottle needs a little syrup to sit where this one sat, and a stronger one needs less of it in the glass.
Drier and stricter: no sherry cask, no solera. In a Sidecar the drink comes out cleaner and sharper, and the raisined sweetness a Spanish-brandy recipe counts on is gone — put it back with a barspoon of syrup.
Sherry
Sherry is a fortified wine; sherry brandy is a strong distillate that has merely been aged in the same casks. One goes into a recipe as a modifier, the other as the base — they do not stand in for each other anywhere.
The solera means a bottle holds spirit of several ages rather than one year: a portion is drawn from the bottom tier and replaced from above. An age on the label here is an average, not a floor.