Heat 1/3 cup each sugar and water in a saucepan until the sugar is dissolved; chill. Puree the cold syrup with 1 cup fresh mint and 1/2 cup fresh cilantro, then strain. Rub the rims of 4 rocks glasses with a slice of jalapeno and a lime wedge; dip in salt and then in sugar. Fill with ice. Combine half of the herb syrup, the juice of 1 lime and 1/2 cup tequila in a shaker; shake, then strain into 2 glasses. Repeat. Top the drinks with ginger beer.
Photograph by Charles Masters