Preheat oven to 325°. In a large bowl, combine flour, sugar, baking powder and salt. In another bowl, whisk together melted butter, egg and vanilla; add to flour mixture and stir to combine. Press onto bottom of a greased 13x9-in. baking dish., For topping, in a large bowl, beat cream cheese and eggs until smooth. Add confectioners' sugar and stir to combine. Pour over crust. Bake until center is almost set and edges start to brown, 40-45 minutes. Cool 1 hour on a wire rack. Sprinkle with additional confectioners' sugar if desired.