Strip leaves from one rosemary sprig and place in cocktail shaker.
Muddle the rosemary leaves gently to release oils.
Add vodka and fresh grapefruit juice to the shaker.
Fill shaker with ice and shake vigorously for 10-15 seconds.
Double strain into an ice-filled highball glass.
Garnish with a fresh rosemary sprig and grapefruit wedge.
Optional: Before filling glass, wet the rim with grapefruit juice and dip in sugar.
Notes
Fresh-squeezed grapefruit juice makes a big difference in taste compared to bottled juice.The cocktail keeps well in a pitcher for 2-3 hours if made in advance. Add ice just before serving.Store extra rosemary sprigs wrapped in damp paper towels in the refrigerator for up to one week.For a non-alcoholic version, replace vodka with club soda or grapefruit-flavored sparkling water.