Muddled blackberries, bourbon, mint, and lemon — deep purple and completely addictive.
Wheated bourbons (Maker's Mark, Larceny, Weller) use wheat as the secondary grain instead of rye. They're softer, rounder, and sweeter — and that sweetness is exactly what plays well against the tart blackberries and lemon juice.
High-rye bourbons (Four Roses, Bulleit, Wild Turkey 101) are spicier and more aggressive. They work, but the spice competes with the berry rather than complementing it. If you only have a high-rye on hand, reduce the lemon juice slightly to soften the tartness.
Replace blackberries with strawberries. Sweeter and less tart — you may want to reduce the simple syrup by ¼ oz.
Use blueberries instead of blackberries. Milder flavour, beautiful deep blue-purple colour.
Add 2 slices of jalapeño to the muddling step alongside the blackberries and mint. The berry-heat combination is genuinely excellent.
Use rye whiskey instead of bourbon. The rye spice against the blackberry tartness creates a drier, more complex drink.