1. Place five basil leaves in a mixing glass. Squeeze the lime into the glass. Press down on the leaves with a muddler and twist 4 to 5 times.
2. Fill glass three-quarters of the way with ice cubes. Add the simple syrup and vodka or gin.
3. Give the glass a good shake and strain into a cocktail glass. Float a piece of the muddled basil on the top as a garnish.

Makes 1 drink.