Place the blackberries into a saucepan, together with the water and sweetener.

Bring to a boil then reduce to a fast simmer, using a spoon to help break the fruit apart. 

After ten minutes, either let the fruit cool in the pan for an hour, or move straight to the next step and strain the fruit pulp out of the liquid using a mesh strainer.

Strain it again through cheesecloth or a coffee filter paper to obtain a clearer liqueur.

Stir in some vodka, brandy, and lime juice. 

Let cool (if needed), then transfer to a bottle and store in the fridge for up to 5 days.