Preheat the oven to 350° F and grease and line a 9-inch square cake pan with parchment paper.
In a large bowl, combine the flour, salt, powdered sugar, and vanilla. Rub the butter into the flour with your fingers until it resembles coarse crumbs. The mixture will be crumbly.
Press the mixture firmly into the prepared pan.
Chill for zo minutes. This helps the crust not shrink as much.
Bake the crust for 20-25 minutes, or until the crust is golden brown on the edges.
Meanwhile, prepare the topping. In a medium-sized bowl, whisk together the eggs and sugar. Sprinkle the flour and salt on top and whisk until fully combined. Whisk in the lemon juice and vanilla.
While the crust is still hot, pour on the topping.Reduce the oven temperature to 325° F and bake for 25-30 minutes, or until the topping is set and just slightly jiggly in the middle.
Allow the bars to cool completely before slicing.