1 Rinse the currants, drain well, and remove from the vines. Add the currants, 150 ml (approximately 5 ounces) of water, and the vanilla sugar to a saucepan. Mix well, and bring to a boil. Reduce the heat and simmer for 15 minutes (or until the berries burst), stirring occasionally.
2 Line a fine strainer with cheesecloth. Place the strainer over a large pot, and pass the fruit mixture through strainer. Drain slowly, and let cool completely. Squeeze the mixture in the cheesecloth to extract all the juice.
3 Measure the juice. Add the appropriate amount of jam sugar (it should be a 2:1 ratio of juice to sugar), then mix until combined. Bring to a boil, and cook the mixture for 4 minutes until the jam begins to thicken. Skim any foam that rises to the surface.
4 Fill the prepared jars to the brim with the jam. Seal tightly and turn upside down to cool slightly. Turn right side up and cool completely.