1. Rinse the cranberries or red currants (lingonberries) if necessary, then combine them with 250ml (8.45 fl oz) of water in a large saucepan.

2. Bring to a gentle boil and cook for about 10 minutes, or until the berries have broken down and released their juice.

3. Skim off any foam that forms on the surface.

4. Add 300g (1.32 cups or 10.58 oz) of granulated sugar to the lingonberry mixture in small increments, stirring constantly until it has fully dissolved.

5. Remove the saucepan from the heat and let the mixture cool slightly to around 55°C (131°F).

6. Transfer it to clean, sterilized jars, making sure to leave a 1cm (0.4 inch) headspace at the top.

7. Secure the lids tightly and store the jam in the refrigerator at a temperature below 4°C (39°F).