Add blackberries and simple syrup to a cocktail shaker and muddle until juicy.
Add vodka (or bourbon), limoncello, and lemon juice. Fill shaker with ice and shake 10–15 seconds.
Strain into a rocks glass packed with crushed ice.
Top with sparkling water or soda water. Stir gently.
Garnish with lemon slice, mint sprig, and extra blackberries if desired.
Notes
Use vodka for a crisp finish, or bourbon for warmth. Adjust simple syrup or limoncello for your preferred sweetness and tartness. Chill the glass for best results. Makes a refreshing summer sipper!