CRUST: Melt butter; mix with confectioners sugar; add flour; mix well. Pat out on pizza pan. Bake at 350 degrees for about 15 minutes, or lightly browned.
FILLING: Beat cream cheese and condensed milk together; add lemon juice and vanilla; pour over cooled crust.
TOPPING: Combine strawberries and cornstarch in a medium saucepan. Cook, stirring, over medium heat until thickened. Cool and spread over cream cheese filling. Top with Cool Whip. Refrigerate.