Preheat the oven to 350 degrees F.
Line a 9 by 13-inch sheet pan with heavy duty aluminum foil, so that the ends of the foil hang over the sides and set aside.
In a bowl, combine 1 1/2 cups of the flour with 1/2 cup of the powdered sugar. Cut in the butter until the mixture resembles fine crumbs. Press in an even layer into the bottom of the pan and bake until pale tan, about 20 minutes. Reduce the oven temperature to 325 degrees F.
While the crust is baking, prepare the filling. (The filling will set up better if the crust is still warm.) In large bowl, beat the eggs and granulated sugar until pale yellow and frothy. Add the remaining 1/4 cup of flour, and the remaining ingredients and whisk to combine. Pour over the warm crust and bake until set, 20 to 25 minutes.
Cool completely on a wire rack. Dust with confectioners' sugar before cutting with a thin, sharp knife into squares.