Muddle blackberries, basil, and simple syrup in the bottom of a cocktail shaker
Add lime juice, tequila, and Cointreau to your shaker
Cover and shake your ingredients
If wanting a salt rim, coat the rim of the cocktail glass with lime juice and roll rim in salt. Fill a rocks glass with ice, and pour your cocktail over the ice
Top with soda water and extra blackberries, lime, or basil leaf for garnish.