Bake the puff pastry shells (unfilled) according to package directions.
Meanwhile, in a medium saucepan, stir together the cranberries, sugar, water, and cornstarch. Turn on heat to medium, cover, and bring to a boil. Let cook for a few minutes until the mixture thickens, then remove from heat and let cool.
Spoon 2 tablespoons of the cranberry mixture into the center of each pastry shell. Garnish with a dollop of whipped cream.