If using fresh blackcurrants, rinse them under cold water and remove any stems.
If using frozen blackcurrants, you can use them straight from the freezer.
Add the blackcurrants, sugar, lemon juice and water to a pot, stir and bring to the boil. Allow it to boil for about 5 minutes, stirring often to stop it from scorching.
Reduce the heat to low and let it simmer and bubble for 10 minutes. It will thicken further as it cools.
Serve warm or allow to cool and store in a sterilised jar in the fridge for up to 5 days (or freeze for up to 2 months).