Sterilise your glass jars by putting them in the oven at 120* for 5 minutes. Set aside for later.

Place the blueberries in a large bowl and with the help of a potato masher, mash them until you obtain the juice.

Transfer the mashed blueberries to a heavy saucepan. Add lemon juice and stir in the pectin.

Bring to a boil over high heat, stirring constantly.

Add the sugar, keep stirring and let it return to boiling.

Cook for 1 minute, mixing.

Remove from the heat.

With a silicone spatula, skim off the foam and with a ladle, transfer the jam into the glass jars.

Let cool down to room temperature for about 1 hour. Cover the jars with the lids and let stand overnight or until set.

Refrigerate for up to 3 weeks or freeze for up to 12 months.