For the cucumber simple syrup:
2 cups granulated sugar
1 cucumber, cut in half and seeded
30 mint leaves
For the drink:
1 1/2 ounces Junipero gin
10 spearmint leaves
10 lemon balm leaves
1/2 teaspoon Kaffir lime zest, optional
1/2 ounce Cucumber Simple Syrup (recipe below)
To make the cucumber simple syrup: Stir sugar into one cup of boiling water until dissolved. Chop one half of the cucumber, and add it and the mint leaves to the mixture. Let syrup sit for a day. Chop remaining half of the cucumber into little, thin half moons. Strain syrup over remaining cucumber.
To make the drink: Chiffonade the spearmint and lemon balm and add all the other ingredients except the seltzer to an empty mixing glass. Fill the glass with ice and shake well.
Add to a Collins glass, top with seltzer, and stir.