Cream the butter until fluffy. Add the powdered sugar and then the vanilla and mix until blended. Remove the mixer from the stand and add in the flour. Mix by hand until the dough comes together and is smooth. Spray the pan with a non-stick vegetable or butter oil spray. Firmly press the dough into the pan. Prick the entire surface with a fork. Bake at 325 for 30 to 35 minutes or untuil the edges are lightly browned. Let the cookie cool in the pan for 10 minutes and invert onto a wooden cutting board. If the Shortbread does not come right out, loosen the edges with a knife and flip again, gently tapping the pan. Cut into desired shapes while still warm.
Recipe by Baking and Eggs at https://bakingandeggs.com/2016/09/25/shortbread-ii/