Slice the vanilla pod lengthwise and scrape out the pulp. Wash, dab dry and clean the strawberries. Depending on how firm and chunky the jam is to be, cut the strawberries smaller if necessary. Place the vanilla pod, pulp and berries in a large bowl and cover with sugar. Cover and leave to cool overnight
Put the strawberry-sugar-mixture in a large pot. Squeeze lemon and add juice. Bring everything to a boil while stirring. When the mixture boils effervescently, continue cooking for about 4 minutes, stirring from time to time. Fill into sterilized glasses with twist-off lids and close them. Place on the lid, turn over again after about 5 minutes and let it cool down
Waiting time approx. 12 hours