Preheat oven to 325 F.
Line a glass 9x9 inch pan with parchment paper (leaving enough overhang to be able to lift the bars out of the pan). Set aside.
To make the crust, in a bowl, combine the butter and powdered sugar until creamy and combined.
Add the vanilla extract, lemon extract and lemon zest.
Stir in the flour and salt, stirring until the mixture turns into a dough.
Gather dough into a ball.
Press the dough evenly and firmly into the prepared pan. (see note)
Bake for 18 minutes.
Remove from oven and prepare the filling.
To prepare the filling combine the egg and sugar in a large bowl and whisk until combined.
Whisk in lemon juice, zest, lemon extract, and vanilla extract.
Whisk in flour until flour is dissolved.
Pour filling into prepare pie crust.
Bake for 25-30 minutes or until middle is set and firm to the touch.
Remove from oven and let cool.
Once cool, refrigerate for about 1 hour (optional but creates an amazing firm texture)
When ready to cut, lift bars from pan with parchment paper. (remove parchment before cutting)
Cut bar in half and then fourths. Cut each fourths into fourths.
Using a sifter, dust bars with powdered sugar and garnish with lemon zest.
Serve cold or room temperature.