Beat butter at medium speed with an electric mixer until creamy; add 2 cups flour and 1/2 cup powdered sugar. Beat until mixture forms a smooth dough. Press mixture into a lightly greased 13- x 9-inch baking pan.
Bake at 350° for 20 to 22 minutes or until lightly browned.
Whisk together remaining 1/4 cup flour, granulated sugar, and next 6 ingredients; pour over baked crust.
Bake at 350° for 28 to 30 minutes or until set. Cool in pan on wire rack. Sprinkle evenly with 1 tablespoon powdered sugar, and cut into bars. Garnish, if desired.