Preheat oven to 325 degrees F.
Crust: In a large bowl, combine 2 cups flour, and confectioners' sugar. Cut in butter with a pastry blender until mixture is crumbly. Press evenly into bottom of a 13 by 9 by 2-inch baking pan. Bake 20 minutes, or until lightly browned.
Filling: In a medium bowl, whisk together sugar, eggs, and juice until well mixed. Add 1/4 cup flour and baking powder, stirring to combine. Sprinkle in some orange zest.
Pour into hot baked crust, and bake 25 minutes, or until set. Cool the bars, so you may top with orange citrus glaze.
For the Orange-Citrus Glaze: Add 4 cups of powdered sugar and 1/2 cup orange juice together, so that it combines to make a nice creamy glaze sauce consistency. Add orange zest. When all ingredients are mixed well, pour onto the citrus bars.