Make the syrup a day ahead and store it in the fridge so assembly is quick. If the foam seems thin, shake the egg white mixture an extra 10 seconds before adding ice. Swap the lavender sprigs for a few drops of butterfly pea extract if you want a deeper purple color without changing the taste.
Course: Drink
Cuisine: American
Equipment: Small saucepan, Cocktail shaker, Strainer, Highball glasses