Preheat the oven to 350 degrees
. In a medium-sized bowl combine the butter, flour, sugar, vanilla, and salt.
Line an 8x8 baking pan with parchment paper (this is important otherwise it will stick) Spray with cooking spray.
Place crust mixture in bottom of the pan and spread out evenly with hands until the bottom of the pan is evenly covered.
Bake for 20 minutes or until crust is a golden brown. Set aside to cool completely.
To Make the Filling
With a stand mixer or a hand mixer, blend together the sugar, butter, and eggs until light and fluffy (about 2 minutes).
Lower speed on mixer and mix in the lemon rind, lemon juice, and basil until incorporated. Slowly mix in flour.
Pour mixture over crust and bake for 40 minutes or until golden brown.
When cool, remove lemon bars from pan and carefully remove parchment paper. Sprinkle with powdered sugar and cut into squares.