Puree the bananas with the lemon juice. Briefly bring to the boil in a saucepan together with 875 ml apple juice. Stir in the sugar.
Stir the cornstarch into the remaining apple juice. Stir this mixture into the soup. Simmer for 2 minutes. Take off the stove, let it cool down and put in a cool place.
Mix the cinnamon with the cream and add to the chilled soup. Then stir in the blueberries.