Rim a martini glass with salt. In a cocktail shaker, combine gin, simple syrup, grapefruit juice, and rosemary sprig. Shake well. Strain into prepared highball glass and garnish with a sprig of rosemary

Rim a highball glass with salt and fill with ice. In a cocktail shaker, combine rosemary, simple syrup, and grapefruit juice and shake well. Strain into prepared highball glass, top with club soda, and garnish with a sprig of rosemary.