1. Place a small plate in the freezer.
2. Add the frozen berries, sugar and lemon juice to a saucepan. Place on a low heat and allow the sugar to dissolve slowly. Once dissolved, up the heat to a boil and stir continuously for 8-10 minutes stirring constantly.
3. To check the jam is cooked, remove the plate from the freezer. Add a 1 tsp of the jam to the cold plate, let it sit for 30 seconds then run your finger through it and if it wrinkles it is ready. Pour into sterilised jars and seal immediately.

This will keep in a cool cupboard for up to a year!