1To make the crust:
In a bowl combine together, the flour and confectioners' sugar. Cut in butter; mix until mixture becomes crumbly and clings together. Press crust mixture into a 13x9x2-inch baking pan. Place baking pan in a preheated 350 degree oven. Bake the crust for about 25 minutes, or until lightly browned.
2To make the topping:
In another bowl beat together, the eggs, sugar, lemon juice, orange juice, and lemon zest. Stir in the 1/4 cup flour and baking powder, mixing well. Pour topping mixture over the baked crust. Place pan in the oven, and bake for an additional 25 minutes.
3When cool; sprinkle the bars with the confectioners' sugar, then cut them into bars. (I cut the bars while they were slightly warm, then sprinkled the bars with the confectioners' sugar.)