First, preheat oven to 325 degrees Fahrenheit. Line an 8 inch square pan with parchment paper.

First make shortbread crust. In a mixing bowl, add melted butter, gluten free flour, sugar and vanilla extract. Stir to combine.

Once combined, press this shortbread mixture down into the lined pan. Bake the crust for 20 minutes.

As soon as the crust comes out of the oven, lightly pierce holes all over. Do not press all the way down, just slightly.

Next, make the filling. Add sifted flour to a mixing bowl. Then, add in all remaining filling ingredients except powdered sugar. Stir until sugar has completely dissolved and no clumps of flour remain.

Pour this lemon filling mixture down over warm crust.

Bake for 20 to 22 minutes or until the middle is set.

Finally, remove from oven. Allow bars to fully cool before topping with powdered sugar. Slice and serve.