Rim your glasses with Kosher salt by rubbing a lime wedge around the circumference of the glass and rolling the edge in Kosher salt.
Fill a cocktail shaker halfway with ice.
Add 4 oz Pantalones tequila, 1 ½ oz lime juice, ¾ oz Cointreau, 2oz blueberry juice, and 1 tablespoon agave to the ice-filled shaker.
Shake for about 15 seconds.
Add ice to your glasses and pour the blueberry margarita over ice, then garnish with sliced lime, a sprig of mint, and fresh blueberries.