For the cherry soup, wash and pit the sour cherries and bring to the boil in a saucepan with the sugar and cherry juice.
Simmer over medium heat for about 10 minutes. Strain the cherries through a fine sieve and bring to the boil again.
Mix cornstarch with a little water until smooth, stir into fruit puree and simmer for another 10 minutes.
Pour soup into 4 cups and chill. Whip the cream with sugar until stiff and garnish the cherry soup with a dollop of each.