In a bowl, toss together the blackberries, sugar, and a pinch of salt.

Cover and let sit in a warm place for 2 hours.

Strain the syrup over a bowl, reserving both the liquid and the berries.

Fill a tall glass with ice.

Add the lime juice, ginger beer, and ½ ounce of the fresh blackberry syrup and stir to combine.

Slowly pour in the rum so it floats on top of the ginger beer.

Garnish with a lime round and a small spoonful of the berries.

Serve.