Soften the cream cheese or mascarpone while you bake the pastry shell according to directions. Let the pie shell completely cool. Spread the cream cheese on the base of the pie shell.
Fill the shell with 3 cups of blueberries.
Combine the remaining cup of blueberries with the water in a small pot over medium heat. Bring to a simmer for 4 - 5 minutes. Strain, reserving all of the juice. Mash the berries to get all the juice out. Discard the berries.
Combine the sugar and corn starch in the same small pot over medium high heat. Gradually stir in the reserved blueberry juices. Cook, stirring constantly until thick and clear. Cool slightly and add the lemon juice.
Pour the syrup over the berries in the pastry shell. Chill.
Serve with whipped cream (I substituted Greek yogurt)
Cooking time does not include baking the pie shell, as that can vary on the package. Approximate time to bake a pie shell can range from 15 to 30 minutes.