Add all ingredients, except sherry, to a cocktail shaker filled with ice. Shake hard and strain into a highball or Tiki glass filled with ice. Float the sweet sherry on top.
There are a lot of variations of this drink. While sherry is traditional, a cherry brandy (such as Cherry Herring) float, is a popular variation. Some versions sub equal parts lemon and lime for lemon. Some swap out the brandy for Pisco. Some swap the light rum for gold rum.
Beachbum Berry Remixed, pg. 48