Combine cornstarch, sugar, water and blueberries in saucepan. Cook over medium heat, stirring until thickened; cool. Combine cracker crumbs into bottom of foil-lined 13 x 9 x 2 inch pan. Mash cream cheese until soft; beat in sugar and vanilla gradually. Fold in whipped topping; drop by spoonfuls over crumb mixture. Spread gently with spatula. Spread blueberry filling evenly over cheese mixture; spread with remaining cheese mixture. Sprinkle with remaining crumb mixture; chill overnight. Use foil to remove dessert from pan. Place dessert on platter; cut into squares. Yield: 15 servings.