Combine 1 cup fresh seedless watermelon chunks and 1/4 cup granulated sugar in a blender. Blend until smooth, then strain through a fine mesh sieve into a small saucepan. Bring to a gentle simmer for 2 minutes to dissolve and slightly reduce. Cool to room temperature and measure out 1 oz for the recipe. (Makes ~3/4 cup syrup; store extra refrigerated up to 5 days.)

In a cocktail shaker, add 2 oz blanco tequila, 1/2 oz St-Germain, 1 oz watermelon syrup, 3/4 oz fresh lime juice, and 4–6 thin jalapeño slices (adjust heat to taste; reserve one slice for garnish).

Add a generous handful of ice to the shaker (about 1 cup). Secure the lid and shake vigorously for 12–15 seconds, until the shaker is well-chilled and slightly frosted.

Double-strain the cocktail into a rocks glass filled with fresh ice using both a Hawthorne and a fine mesh strainer to remove jalapeño seeds and pulp. Alternatively, serve straight up in a chilled coupe if preferred.

Rim & Garnish

On a small plate, mix 1 tsp Tajín and 1/4 tsp coarse sea salt (optional). Wet the rim of the serving glass with the lime wedge, then dip the rim into the Tajín mixture to coat evenly.

Garnish the finished cocktail with the reserved thin jalapeño slice and a small watermelon wedge or skewer. Serve immediately.