Fill a shaker with ice cubes. Add all ingredients. Shake and strain into a chilled rocks glass filled with crushed ice.
Bartenders often have two different ice machines: one for cubes and one for crushed ice. It's fairly easy to make crushed ice at home. Put ice cubes in a towel, secure by folding the fabric so the ice stays in it. Then gently pound the ice with a hammer until your ice crush looks perfect. Easy!