Muddle fresh blackberries, lemon juice, mint leaves, and sugar in a highball glass.
Stir in the whiskey.
Add ice (crushed if possible) and top with wheat beer.
Optional garnish
If you’re feeling fancy, cut a wooden skewer so that it’s slightly taller than your glass. Thread 4-5 blackberries onto the skewer and add them to your cocktail along with a sprig of fresh mint.