Rinse the strawberries, pat dry and remove the stems. Depending on the size, cut into quarters or halves.
Pour the cut strawberries with the jam sugar in a pot, stir and cook for at least 2 hours. Then add the lemon juice and stir 3-4 min. Boil and skim off the foam.
Pour the filling into the prepared jars and let sit for about 15 minutes. Put on cover and let cool.