First, prepare the lavender syrup: In a sauce pan over medium low heat, combine 2/3 cup water, 2/3 cup granulated sugar, 2 Tbsp agave, and 2 Tbsp dried lavender. Stir occasionally and allow sugar to dissolve. Allow to cool for 10 minutes before straining into a container. Store in the fridge for up to 1 month.
To make the drink: Combine 2 oz Tequila, 0.5 oz Cointreau, 0.75 oz lavender simple syrup, and 5-6 muddled blackberries in a shaker with ice. Shake well and strain into a salt-rimmed glass. Garnish with extra blackberries. Serve and enjoy.
