Add vodka, prickly pear juice, lime juice, and simple syrup to the shaker.
Strip leaves from one rosemary sprig and add them to the shaker.
Shake hard for 15 seconds until well chilled.
Double strain into a Collins glass filled with fresh ice.
Top with club soda and stir gently.
Garnish with remaining rosemary sprig and lime wheel.
Notes
Store-bought prickly pear juice works well, but fresh juice gives the best flavor. Look for ripe prickly pears at Mexican grocery stores.Make simple syrup by combining equal parts sugar and water in a pot. Heat until sugar dissolves, then cool completely.The drink can be made non-alcoholic by replacing vodka with extra club soda.Keep rosemary sprigs fresh by storing them wrapped in damp paper towels in the refrigerator.