2 teaspoons lemon juice (about 1/2 lemon), plus 2 thin lemon slices, for garnish
2 dashes lemon bitters
In a cocktail shaker filled with ice, combine the grapefruit juice, vodka, elderflower liqueur, lemon juice and lemon bitters and shake well. Strain into 2 coupe glasses. Float a thin lemon slice on top of each.