This recipe makes about 5 - 250 ml jars.
2 1/2 lbs blueberries
4 2/3 cup sugar, plus 1/2 cup
3 1/2 oz water
7 oz lemon juice
Rinse the two lemons in cold water and slice them into thin rounds. In a preserving pan, poach the lemon slices with 1/2 cup of sugar and the water. Continue to cook until the slices are translucent.
Rinse the blueberries in cold water without soaking them. Add the blueberries, 4 2/3 cup of sugar and the lemon juice to the pan and bring to a simmer. Pour into a ceramic bowl. Cover with a sheet of parchment paper and refrigerate overnight.
Next day, bring this preparation to a boil, stirring gently. Continue cooking on high heat for about ten minutes, continuing to stir. Skim carefully. Return to a boil. Check the set. Put the jam into jars immediately, add the lemon slices to the jars and seal. Process in a boiling water bath for ten minutes.