Chill glasses of choice in the freezer for a few minutes or add ice cubes to them. Discard ice cubes prior to filling the glass.
Fill a shaker with ice and add gin, Key lime juice and simple syrup. Shake until chilled.
Strain into a chilled coupe or Nick and Nora glass (if serving ‘up’) or into a rocks glass filled with fresh ice.
Garnish with a Key lime slice.
Notes
* Key limes are available all year round – you can substitute traditional lime juice. * If you have extra lime juice, freeze it for a future cocktail. SIMPLE SYRUP 1 cup (8 ounces) water 1 cup granulated sugar Bring the water to a simmer in a saucepan set over medium-high heat. Add the sugar and stir until it completely dissolves. Remove the pan from the heat. Set aside to cool to room temperature. Pour the syrup into a clean 1-pint bottle, cap it and refrigerate it until needed. Makes 1½ cups and keeps two months or longer in the refrigerator.