Rub the rim of two glasses with lime. Swirl rim of glass in either salt or sugar - your preference.
In a cocktail shaker, muddle the blueberries in the lime juice until every blueberry is pulverized. Add the tequila, simple syrup, bitters, a few ice cubes and the remainder of the lime used to rub the rim of the glasses to the shaker.
Shake vigorously and strain into the prepared glasses.