Gather the basil leaves and muddle them in the base of a shaker. If you don’t have a muddler or a shaker, just use the back of a wooden spoon and a mug – it works just as well.
Once you’ve thoroughly muddled the basil, add the other ingredients and shake with a few cubes of ice. Finally, strain into an ice-filled glass. Add a few basil leaves to garnish, et voila!