Put blueberries and juice in a pot. Add vanilla sugar and bring to the boil while stirring. Mix cornflour with some cold water and stir into the blueberry juice mixture. Bring to the boil while stirring once.
Chill the soup.
Core and peel the melon. Cut melon into slices. Arrange the blueberry cold peel with the melon boats and the meringue dots as foam crown.