Red grapefruit juice and orgeat give this drink its slightly opaque, pearlescent color. If you choose, add a splash of rum or vodka, but this floral, citrusy blend can hold its own without the booze.
What to buy: Orgeat is an almond-sugar syrup traditionally made from whole blanched almonds. The nut oil gives the syrup (and cocktails made with it) a richness that can’t be duplicated with a cheap almond-flavored syrup. Try to find a high-quality brand such as Small Hand Foods or B.G. Reynolds.
Place the grapefruit juice, lime juice, and orgeat in a cocktail shaker and fill it halfway with ice. Shake vigorously until the outside of the shaker is frosted. Strain into the chilled glass and garnish with the grapefruit slice.