For the blackberry jam, carefully wash the blackberries and pat dry.
Mash the blackberries with a fork and boil once with 3 tablespoons of water. Pass through a sieve so that the seeds are removed.
Bring the blackberry puree to a boil with the preserving sugar in a large saucepan and simmer for 4 minutes until bubbling.
Finally, stir in the vodka and bring to a boil again.
Immediately fill the blackberry jam hot into glasses and seal.