Gently muddle blackberries and rosemary in a cocktail shaker.

Add the tequila, lime, simple syrup and ice cubes. Cover and shake until cold.

Strain cocktail into glasses over ice and garnish with additional berries and rosemary.

*To make simple syrup, whisk 1 cup sugar and 1 cup water in a pot over medium heat. Bring to a boil and stir until sugar is dissolved. When the liquid is completely clear, remove from heat and cool. Store in an airtight container for up to two weeks.