Preheat the oven 350 degrees F. and set aside an 8x8-inch square baking pan sprayed lightly with cooking spray.
In a medium bowl, combine together the flour, butter, powdered sugar, vanilla, and salt using a spoon until it begins to come together and then gently knead it by hand until all of the dough sticks together.
Form into a ball and place into the prepared baking pan and press down in the bottom of the pan evenly. Wet your hands a little to prevent sticking.
Using a fork, prick the dough all over to help the dough cook evenly and so no bubbles will form.
Place the crust into the preheated oven and bake 15 to 20 minutes, until the crust is light golden brown and then remove from the oven.
While the crust is baking, in the same bowl the dough was in whisk together the eggs, egg yolk, granulated sugar, flour, lemon juice, and lemon zest until it is fully combined and pour over top of the finished baking crust. It is fine if the crust is still warm from baking.
The lemon mixture will be liquidy, but it will firm up so place back into the oven and continue to bake the lemon bars for 20 to 25 minutes until the edge of the bars is golden brown and the center is set.
Remove the lemon bars from the oven and allow them to cool completely in the dish on a cooling rack before you slice into small squares.