Put the jam jars in hot (preferably almost boiling) water. Wash the currants and use a fork to strip them off the stalks. Wash the strawberries and remove the greens. Take the jam jars out of the water, turn them upside down on a kitchen towel and let them drain. Put the berries in a saucepan and chop up with a hand blender. Mix the berries with the preserving sugar, bring to the boil and continue to simmer for 5 minutes while stirring. Immediately pour the mixture into the jars, close them immediately and place on the lid for about 5 - 10 minutes. Then turn it over and let it cool down.