Place a plate in the freezer to test the jam later.
Add all the ingredients to a large saucepan over a medium heat.
Stir the ingredients constantly until the blueberries start to soften, then crush them using a potato masher.
Once the sugar has dissolved, bring the jam to the boil and boil for 5 mins.
Test the jam by putting a small spoonful on the chilled plate. If after 30 secs a skin has formed, the jam is ready. If not, boil for a further 2 minutes and check again. Repeat until ready. Be careful not to over boil the jam or it will end up too thick.
Remove from the heat and skim off any scum which has formed on top and discard.
Let the jam sit for 5 mins and then ladle into hot sterilised jars with the help of a funnel.
Place a wax disc on top of the jam and cover with a lid.
To sterilise your jars, wash the jars and lids in warm soapy water and rinse. While still wet, place them upside down on a baking tray and pop them into a preheated oven at 180°C/160°C fan for 15 mins.
