Muddle the Ingredients: In a cocktail shaker, combine the blackberries, mint leaves, lemon wedges, and simple syrup. Muddle them together using a muddler or the back of a spoon to release the juices and oils.

Add the Whiskey: Pour in the whiskey over the muddled mixture.

Shake Well: Fill the shaker with crushed ice and shake it vigorously until well-mixed and chilled.

Strain and Serve: Strain the mixture into a glass filled with crushed ice. You can use a fine-mesh strainer if you prefer a cleaner drink without seeds.

Top It Off: If you like a bit of fizz, top off your cocktail with a splash of club soda.

Garnish: Garnish with a couple of whole blackberries, a sprig of mint, and a slice of lemon.