In a medium saucepan, combine cornstarch and sugar over medium heat. Gradually stir in water, then add fresh raspberries and a squeeze of lemon juice. Cook until thickened.

In a mixing bowl, combine melted butter with graham cracker crumbs and a bit of sugar. Press into the bottom of a 9 x 13-inch dish to create a crust. Bake at 350°F for 8-10 minutes.

Beat cream cheese with powdered sugar, milk, and vanilla in a large bowl until smooth. Fold in Cool Whip gently.

Spread the cream cheese layer over the cooled crust, then spoon the cooled raspberry filling on top.

Cover and refrigerate for at least 6 hours or overnight to set.