I’m calling this one Border Callie, in reference to both the inclusion of the Greyhound-like grapefruit juice and the fact that mezcal originates south of the border:
1 1/2 oz fresh-squeezed grapefruit juice
1 oz mezcal (I used Del Maguey Vida)
1 oz St. Germaine
1/2 oz lime juice
1 bar spoon simple syrup (or maybe agave if you have it?)
2 dashes grapefruit bitters
Shake it good with ice and strain into a coupe.