Remove rosemary leaves from spring and muddle into the bottom of a cocktail shaker with agave.
Add grapefruit, lime, lemon, alcohol and 1 cup ice to a shaker. Shake vigorously until ice cold.
Rim glass with black or white cocktail sugar.
Pour into a martini glass or strain into a cocktail glass with fresh ice. Garnish with a rosemary sprig and fresh grapefruit zest.
Notes
If you prefer a mocktail; remove the alcohol and replace it with a splash of tonic or flavored sparkling water. Don't add the tonic or sparkling water until after shaken.