Preheat oven to 325°. Line the bottom and sides of a 9x13 pan with parchment paper, leaving an overhang on the sides so you can lift the finished bars out to cut easily into equal squares.
Mix the crust ingredients above and press into prepared pan. The dough will be thick, so press into an even layer. Bake for 18-20 min until you see slight browing around the edges. Remove from the oven and set aside while you prepare the lemon filling.
If you don't use the frosting, once the bars are cooled, sprinkle with confectioners sugar. They look great and ready to eat!
I use a glass dish to bake these bars. You can use a metal pan too if that is what you have.
You can easily cut this recipe in half - it will still make 16 bite size servings. Enough to share.
Keep refrigerated - they will last one week.
Make the filling by sifting together sugar and flour (this ensures you have no lumps in the filling). Add the eggs and lemon juice and mix until completely combined.
Pour the filling over the baked crust and bake for 22-25 minutes until they are not jiggling in the center. Remove from the oven and allow them to come to room temperature before setting in the refrigerator for 2 hours, or until chilled throughout.
Once cooled, you can easily lift the parchment paper to remove the bars from the pan.
Optional frosting - Beat butter, powdered sugar and milk for 6-8 minutes on high speed. Then add 2 T. cold water one at a time. Beat until smooth. Spread over cooled bars.