This vibrant drink combines fresh mint and blackberries with sparkling wine and tequila.
In a medium saucepan, heat the sugar and 1 cup water over medium, stirring, just until the sugar dissolves. Let the simple syrup cool for 2 minutes.
Strip the leaves from 8 mint sprigs. (You should have about 1 cup of leaves.) In a blender, puree the mint leaves, simple syrup, and berries; using a fine-mesh strainer, strain into a large pitcher. Cover and refrigerate until cold, about 45 minutes. (The syrup can be refrigerated for up to 3 days.)
Stir the tequila, bitters, and 1 1/2 cups cold water into the pitcher. (If not serving right away, cover and refrigerate for up to 1 day.)
Stir the lime juice into the pitcher. (If not serving right away, cover and refrigerate for up to 2 hours.)
Stir the cocktail. Pour into glasses filled with ice. Top each drink with a splash of sparkling wine. Garnish with the remaining mint sprigs.