In a medium bowl, combine graham cracker crumbs, 1/4 cup sugar, and melted butter. Press the mixture into the bottom of a 9×13 inch baking dish to form a crust. Chill in the refrigerator while preparing the filling.

In a large bowl, beat the cream cheese until smooth. Add powdered sugar and vanilla extract; beat until creamy. Gently fold in the whipped topping. Spread this mixture over the chilled crust.

In a saucepan, mix the blueberries, 1/2 cup sugar, cornstarch, water, and lemon juice. Cook over medium heat, stirring constantly until the mixture thickens and becomes clear.

Pour the hot blueberry mixture over the cream cheese layer. Smooth it out to cover the filling evenly.

Refrigerate the dessert for at least 4 hours, or until set.