Preheat oven to 350 degrees F and put the rack in the middle position.
Cut each stick of butter into eight pieces. Zoop it up with the flour and the powdered sugar in a food processor until it looks like coarse cornmeal (just like the first step in making a piecrust.) Spread it out in a greased 9x13 inch pan (that’s a standard sheet cake pan) and pat it down with your hands.
Bake at 350 degrees for 15-20 minutes, or until golden around the edges. Remove from oven. (Don’t turn off oven!)
Mix eggs with white sugar. Add lemon juice (and zest, if you want to use it.) Add salt and baking powder and mix. Then add flour and mix thoroughly. (This will be runny - it is supposed to be.)
Pour this mixture on top of the pan you just baked and stick it back into the oven. Bake at 350 degrees F for another 30 to 35 minutes. Then remove from the oven and sprinkle on additional powdered sugar.
Let cool thoroughly and cut into brownie-sized bars.