In a small mixing bowl, cream butter and 2 T sugar. Gradually add flour and mix well. Press onto the bottom of a 13-in x 9-in x 2-in baking dish coated with cooking spray. Bake at 350 degrees for 12-14 minutes or until set and edges are lightly browned. Cool on a wire rack.
In a large mixing bowl, beat cream cheese and confectioners' sugar until smooth. Fold in whipped topping; spread mixture over crust. Refrigerate for 20 minutes.
Meanwhile, in a large saucepan, combine cornstarch and water until smooth. Stir in blueberries and remaining sugar. Bring to a boil; cook and stir for 2 minutes or until thickened. Cool to room temperature.
Spoon topping over cream cheese layer. Cover and refrigerate for at least 4 hours. Cut into squares.