Brandy of course is the distillate from the fermented fruit. In this case you would ferment blackberries ,Just make dry blackberry wine, and then distill. I have made many fruit brandies this way. One that pleases my firends is an apple brandy that compares with Calvados. Kirschwasser is made this way. Oh, use a potstill to retain the smell and taste of the fruit.

Otherwise you could make a blackberry schnaps. Not the over sweet stuff they drink in the US. I mean a good German type. Soak fruit in alcohol, in this case the blackberries, and then redistill. Again use a pot still. You will be amazed at the fruit essences that will come over in the distillate.

It will take less fruit to make the schnaps then if you make the brandy. You can try mixing alcohol and fruit wine also. ApfelKorn is made by mixing apple cidre with grain alcohol ,Korn,.

It depends on the fruit. I find that about 1/2 litres of blackberries works well depending on the amount of alcohol you have. I soak the balckberries in about 6 litres of 30 to 40% alcohol and then redistill. This gives a light flavor. Start with clean tasteless alcohol as much as possible. I dilute with distilled water to make sure the still won't boil dry.

If you don't want a clear product just soak the fruit and then drink. Some like to add sugar.