1. While the crust is baking, prepare the filling so it will be ready to be poured on the hot crust as it is done. (This prevents the filling from absorbing into the crust.) In a stand mixer, mix the eggs with the sugar, then add the lemon juice and zest to combine. Add the baking powder and mix thoroughly, without incorporating too much air. (You don’t want it to get frothy.) The mixture will be liquidy.
2. Pour the lemon mixture over the hot crust and return to the oven to bake for 20-30 minutes. Check on it after 10 minutes, and if the top is starting to brown excessively, cover loosely with foil. Lemon squares are done when filling is slightly jiggly when you shake the pan, but not liquid.
3. Allow to cool to room temperature and cut into even, small squares, and sprinkle with confectioner’s sugar.