Cut the cleaned strawberries into small pieces, add the blueberries and lingonberries and puree them, add them to a large saucepan with sugar and lemon juice and let stand for about 20 minutes until the fruit has pulled juice and the sugar has dissolved. Bring to a boil.
Let simmer for four minutes while stirring. Possibly add rum shortly before the end of the cooking time.
Make a gel test on a plate.
Then immediately pour the jam into jars that have been rinsed with hot water and close.