Prepare a pie crust and refrigerate for at least half an hour. Roll out the crust, place in a 9-inch pie dish, and bake at 375 for 10-15 minutes.
In a saucepan, combine 2 cups of blueberries, 1/2 cup of water, lemon juice, sugar, and ginger. Heat over medium-low until the mixture begins to bubble and the berries burst.
In a small bowl, mix the cornstarch with 2 Tablespoons of water; pour slowly into berry mixture, stirring all the while. Let the berry mixture thicken and bubble for a few minutes. Remove from heat and cool slightly.
Pour remaining 3 cups of blueberries into the slightly cooled pie crust. Pour cooked berry mixture over and spread with a spatula. Chill the pie thoroughly in the refrigerator. Before serving, beat the whipped cream and sugar and spread over the pie.