Line the bottom and sides of a 9×13 glass baking pan (do not use metal) with parchment paper, leaving an overhang on the sides to lift the finished bars out
Combine melted butter, sugar, vanilla extract, and salt in a medium bowl. Add the flour and stir to completely combine. The dough will be thick. Place crust firmly into prepared pan, making sure that it is even and nice.
Place the baking dish in the oven and bake for 20-22 minutes or until the edges are lightly browned. Remove from the oven. Prick holes all over the warm crust with a fork (but do not go through the crust).
Whisk all the filling ingredients together until combined.
Pour filling over warm crust. Bake the bars for 20 minutes or until the center is relatively set and no longer jiggles.
Remove bars from the oven and cool completely at room temperature.
Once cool, lift the parchment paper out of the pan using the overhang on the sides.
Dust with confectioners’ sugar and cut into squares before serving.