In a medium saucepan, combine the fresh blueberries, granulated sugar, lemon juice, cornstarch, and water. Stir gently to combine.
Cook the mixture over medium heat, stirring frequently, until it comes to a boil. Continue to cook for an additional 2-3 minutes until the mixture thickens. Remove from heat and stir in the vanilla extract. Allow to cool to room temperature.
While the blueberry mixture cools, prepare the whipped cream. In a mixing bowl, beat the heavy cream, powdered sugar, and vanilla extract until soft peaks form.
Once the blueberry mixture has cooled, pour it into the pre-made graham cracker crust, spreading it evenly.
Top the blueberry filling with the whipped cream, spreading it gently to cover the blueberries completely.
Refrigerate the dessert for at least 2 hours before serving to allow it to set properly.