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You'll need a large glass jar that can hold at least a quart (4 cups). The jar should have a sealable lid since you'll be storing the brandy in it and shaking it frequently. Place 2 cups (44g) of blackberries into your clean jar and smash them a little with the end of a wooden spoon to release some juice. If you like your blackberry brandy to be a little tart, add 1/2" piece of lime zest to the jar. Buy an unflavored vodka and brandy. Any quality brandy will work when making homemade blackberry brandy, especially if you let the blackberries infuse the alcohol for several months. Pour 3/4 cup (177 ml) of brandy and 1 1/4 (355 ml) cup of vodka into your jar with the muddled blackberries. For a stronger brandy flavor, you can replace the vodka with more brandy or even whisky, rum, or gin. Seal the jar with your berries, vodka, and brandy. Shake the mixture and let it sit for 3 days. Avoid refrigerating it and keep it out of direct sunlight. After 3 days, pour the brandy mixture through a strainer lined with cheesecloth. This will catch any blackberry solids. You can throw away the blackberry solids since they'll mainly be seeds. Mix 1 cup (235 ml) of water with 1 cup (200g) of granulated sugar in a small saucepan. Cook it over medium heat until the sugar dissolves. Refrigerate the syrup until it's cool. Add all of the cold simple syrup to your strained blackberry brandy. If you want to make extra simple syrup to further sweeten the brandy or to use in other drinks, you can double the water and sugar. Refrigerate your extra simple syrup for up to 5 days. Shake the jar so that the simple syrup and blackberry brandy completely mix. Let it rest for at least 1 day after you add the syrup. You can then serve the blackberry brandy or mix it into a cocktail. Refrigerate your blackberry brandy for up to 2 months.

Summary:
Muddle your blackberries. Add your alcohols. Shake and strain the infused brandy. Make a simple syrup to add to the brandy. Store your blackberry brandy.