Prepare the blackberries – Wash the berries thoroughly and remove any stems or damaged fruit.

Cook the fruit – Place the blackberries and water in a large saucepan and cook over medium heat until the berries soften.

Mash the berries slightly – Use a spoon or potato masher to break down the fruit and release juices.

Add sugar and lemon juice – Stir in the sugar and lemon juice until the sugar dissolves completely.

Bring to a rolling boil – Increase the heat and allow the mixture to boil rapidly for about 10–15 minutes.

Test the jam set – Drop a spoonful onto a chilled plate. If it wrinkles when pushed, the jam is ready.

Remove foam – Skim off any foam from the surface for a smoother jam.

Fill sterilized jars – Carefully ladle the hot jam into sterilized jars.

Seal and cool – Close the jars tightly and allow them to cool completely.