This 50’s classic is essentially a fizzy Gin Sour. Cocktail wizard Gaz Regan suggests a lovely variation: instead of using simple syrup and lemon juice, muddle a heaping tablespoon of granulated sugar with a half a lemon in wedges, caipirinha-style.
Shake everything but the sparkling water with ice, and strain into an ice-filled glass (a Collins glass, naturally). Top with sparkling water.
If you want to make it the way Regan suggests, simply do your muddling and then build the drink in the same glass.
The classic garnish is a cherry and a half-wheel of orange.