First, grate the currant and put it in a large pot – about 7 liters. Using a potato masher, mash the currant so that liquid comes out.
Add 200 g sugar, stir and let stand for a few hours. Put the currant mixture through a whisk to get the seeds out.
Return mixture without seeds to large saucepan, add remaining sugar and boil until bubbly, about 10 minutes, repeatedly lifting off foam and pouring away. Make a jelly test.
Pour into clean jars and seal with twistoff lids. Currant does not need jelling sugar to jell!