Chill your cocktail glass—just fill it with ice and water while you make the drink.
Put the basil leaves in your shaker and gently muddle them. You want to release the oils, not turn them into mush.
Add gin, lime juice, and simple syrup to the shaker.
Fill the shaker about three-quarters full with ice.
Shake hard for about 15 seconds, until the outside gets frosty.
Dump the ice water out of your glass.
Double-strain the drink into your chilled glass.
Garnish with a basil leaf and a lemon slice.
Notes
Herb-forward gins like Hendrick’s or The Botanist play really nicely with basil here. If you don’t love sweet drinks, you can drop the simple syrup down to ½ oz.Want a mocktail? Swap the gin for cucumber-infused water or a non-alcoholic gin like Seedlip. It actually works surprisingly well.You can make the cocktail ahead—just mix everything except the ice and stash it in the fridge for up to 8 hours. When you’re ready, shake with ice and strain.For a crowd, batch the base (no ice) and keep it cold. When it’s time to serve, shake each drink with fresh herbs for the best flavor.