Select the blueberries, wash and drain well. Weigh 1 kg blueberries. Squeeze lemon. Cut the vanilla pod lengthwise and scrape out the pulp. Mix blueberries, lemon juice, vanilla pulp and jam sugar in a large pot.
Then mash roughly with a potato masher. Add the vanilla pod.
Bring everything to the boil while stirring constantly at high heat. Then boil for about 4 minutes while stirring continuously until bubbly. Remove the vanilla pod. Immediately fill jam to the brim into prepared jars with twist-off lids, close them and let them cool down upside down.
The jam lasts 6-9 months.