4 cups water
Combine blackcurrants and water in a large saucepan. Bring to the boil and cook for 10 minutes. Add sugar and bring back to the boil, stirring until sugar has dissolved. Add butter. Boil hard for 10 minutes or until setting point is reached.
Allow to stand for 5 minutes, then pour into sterilised jars and seal. The jam can be eaten as soon as it cools.