Preheat the oven to 350°F. Line the glass baking dish with parchment paper.
In a medium bowl, cream together the softned butter and 1/2 cup of sugar. Mix in the 1 1/2 tsp vanilla extract, 2 cups of flour and 1/4 tsp salt. Keep mixing until the mixture is crumbly.
Spread the dough evenly into the bottom of your prepared pan. Press the dough with your fingertips to flatten and even out.
Bake crust 15-20 minutes or until lightly golden brown at the edges. Set on wire rack and let cool slightly while you mix the filling.
***While your crust is baking you will want to zest and squeeze the lemons. ***
In a large mixing bowl, whisk together eggs and sugar. Add lemon juice and lemon zest and whisk until combined. Add 1 cup of flour and whisk until smooth and very well blended.
Pour the filling over the crut and bake in the center of the oven at 350°F for 30-35 minutes or until the filling is set. Just until the filling is no longer wobbly in the center.
Cool in th pan at room temperature for at least 1 hour then refrigerate for at least 2 hours before serving.
When you're ready to serve, pull the parchment paper up slightly to loosen from the pan then transfer to a cutting board and cut into 12 - 16 squares, then dust the tops with powdered sugar.