Blackberry jam - I need a foolproof recipe please...

[HattieFranks]

I have 1kg of blackberries and 1 kg of jam sugar. What next?

Thanks

About a tablespoon of lemon juice for each kg of blackberries (I think - google) which helps the pectin. Cook the blackberries a bit first to soften them, then put in the sugar, stir on a low heat to dissolve, then bring to a boil until you reach setting stage. Blackberry jam is my have

You can also add apple, or get a bottle of pectin. Blackberry jam won't set on its own as blackberries are very low in pectin.