If using canned cherries, drain the jar but keep the juice. Add water to the juice that that you have 2 cups/500ml of liquid. If using frozen cherries, use water instead.
Remove 6 tablespoons of liquid and mix with the cornstarch, sugar, and vanilla extract to form a thick paste.
Heat the remaining liquid in a small saucepan and bring to a boil. Once boiling, remove from heat and stir in the cornstarch paste. Stir continuously with a whisk.
Place back on the heat and boil for another 1-2 minutes. The liquid will become thick and paste-like.
Add the cherries and warm through. Leave to cool and refrigiate until needed
Making the Whipped Cream
Pour the chilled cream, vanilla extract, and sugar into a tall mixing bowl.