In a bowl add in sugar, lemon zest, salt and flour. Whisk them together very well.
Juice the lemon to get 1/4 cup of juice and add it to the flour mixture.
Add in the eggs and vanilla extract and whisk all of them together really well. Don't skip the vanilla extract because it gets rid of the egg smell.
Pour the filling over warm crust and bake for about 20 minutes or until the filling is just set. It means the top is white and when you gently shake the pan, you'll see a very slight jiggle in the center. The center will continue cooking as the filling is cooling down.
Let the pan cool down on a wire rack completely, about an hour, and then refrigerate for 2 hours or overnight.
Grab the overhang parchment paper and slowly lift the lemon bar out of the pan. It sometimes get a little sticky on the sides but don't panic it will come out.
Use a large knife and cut it to squares, wiping off your knife after each cut.
Sprinkle with powdered sugar and more lemon zest if you like.