For simple syrup (make in advance): Add water and sugar to a small pot over medium heat. Stir regularly and bring to a slight simmer. Remove from heat and let cool completely before using.
TIP: If you’re in a rush, you can transfer the hot simple syrup to a metal mixing bowl and place the bowl in a larger bowl full of ice water. Stir the simple syrup and it will chill in a few minutes.
To make a cocktail: Combine ingredients in a cocktail shaker with a good amount of ice. Shake vigorously for 30 seconds. Strain into a chilled glass.