1 kg Fruit
1 kg Chelsea Jam Setting Sugar
A knob of butter (10g)
Crush the fruit coarsely with a potato masher, fork or food processor. Or I simply heat the frozen berries until they are a bit mushy.
Put the fruit and jam setting sugar into a large, heavy based 6 litre pot (I used a preserving pan). Heat over a low heat until the sugar is dissolved, stirring occasionally with a wooden spoon. Do not allow to boil.
Add a knob of butter then increase heat and bring to a full boil (a boil that cannot be stopped when stirred). Boil for 4 minutes only, carefully skim off any foam from surface during cooking. Spoon out a small amount of jam onto a cold plate. Allow to cool slightly, then test for set: push finger gently through jam, when surface wrinkles remove the pot from heat. Bottle immediately into sterilised jars.