Pit the cherries and cook in a little water until tender. Strain until 5 cups (based on preparation with 400 g of sour cherries) of juice are obtained. Add sugar and salt and bring to a boil.
Melt cornstarch in water, stir until smooth and add to boiling juice, stirring throughout. Bring back to a boil.
Rinse a stone or porcelain mold with water, sprinkle with sugar and pour in the juice. Chill.
Bring to table with whipped cream and serve with sugar.