Makes 6–8 cocktails
1 medium English cucumber
1 small watermelon
2 cups sugar
2 cups water
1 bunch fresh mint, plus more for garnish
6 limes, juiced
Whiskey, tequila, aged rum, and/or vodka
3 tablespoons tajin, a Mexican spice blend available in most supermarkets
Lime wedges, thinly sliced jalapeños, and thinly sliced watermelon radishes for garnish
Peel and cut cucumber into chunks. Cut watermelon in half, remove seeds, and scoop out flesh (aim for about 5 cups). Puree cucumber and watermelon in blender. Strain through a fine-mesh strainer, pressing on any solids. Pour into small pitcher or jar and place in refrigerator to chill.
Place water and sugar in a medium saucepan set over medium-high heat. Heat until simmering and sugar is fully incorporated, stirring gently. Pour hot syrup over the mint in a heat-resistant bowl. Let sit for 10 minutes. Strain syrup into a small pitcher or jar and place in refrigerator to chill.
For each cocktail, fill a small cocktail shaker with ice. Place tajin in a small dish. Moisten rim of cocktail glass and press gently into tajin. Pour 1 ounce watermelon-cucumber juice, 1/2 ounce mint syrup, 1/2 ounce lime juice, and 1/2 ounce spirit of choice. Shake gently in shaker with ice and strain into glass. Garnish with your choice of lime wedge, mint sprig, radish, or jalapeño.