Put the washed blackberries and the water into a thick bottomed saucepan. Simmer for around 10 - 15 minutes to soften the fruit.

Add the golden caster sugar and bring to the boil slowly.

Add the pectin, then allow the jam to rapid boil for around 5 minutes. Add the butter.

You might have some scum to scoop off the top, or you might not have. Whichever way, let the jam settle for a few minutes after turning off the heat, and place it into clean and sterilised jars for storage.