Zest and juice (3 to 4 tablespoons) of 1/2 grapefruit, plus 2 wedges, for garnish
4 ounces white rum
Club soda, as needed
In a cocktail shaker, muddle the lime juice, sugar, mint leaves and grapefruit zest until the mint is bruised and the sugar starts to melt. Add the grapefruit juice and rum. Fill with ice and shake until very cold. Strain into 2 glasses over ice and top off with the club soda. Garnish with a mint sprig and grapefruit wedge in each glass.