Preheat oven to 350F and line a 8” glass, square baking dish with parchment paper. Leave a bit of parchment to overhang the sides for easily removal after baking.
In a medium bowl, whisk together the flour, salt, and sugar for the shortbread crust.
Use a pastry cutter or two forks to cut in the softened butter.
Once incorporated, press the shortbread crust into the prepared baking dish. Bake for 25-30 minutes, or until lightly golden brown.
While the crust is baking, prepare the lemon filling. Whisk the eggs together in a medium bowl.
Sift the sugar, flour, and salt together and add in with the eggs. Whisk to combine.
Whisk in the vanilla, lemon juice, and lemon zest. Set the filling mixture aside until all the bubbles are gone (about 15 minutes).
Once the crust is done baking, pour the lemon filling onto the hot crust.
Lower the oven temperature to 325F and bake an additional 30 minutes, or until the filling is set.
Once completely cooled, remove the bars from the pan and cut into squares. Dust with confectioners sugar if desired.