Amazing Scottish Shortbread

1. In a large bowl (or in the bowl of a stand mixer), beat the butter, vanilla and powdered sugar together with an electric mixer (use the paddle attachment on a stand mixer, if using) until combined. 2. Gradually add the all-purpose flour, cake flour and salt and mix until just combined (don't over mix the dough). 3. Press the dough into a rectangle shape about 1 1/2 inches high (see pictures below) on a parchment lined baking sheet. Cover with plastic wrap and refrigerate until firm, about an hour. The dough can e refrigerated for several days. Alternately, if you want to cut the shortbread into different shapes (other than a thin rectangle), press the dough into a disc-shape and cover with plastic wrap and refrigerate (similar to how you would do it if refrigerating sugar cookie dough or a pie crust). 4. Once firm, take a large, sharp knife or the straight edge of a bench scraper and cut the long rectangle dough into 1/4-inch slices (again, see picture below). If the cookies aren't perfectly straight not he edges, press them into an even shape or trim the edges. Otherwise, roll the dough out on a lightly floured countertop to about 1/4-inch thickness and cut into desired shapes. 5. Place the cut cookies about 1-inch apart on a parchment or silpat-lined baking sheet. Prick each cookie a few times with the tines of a fork. 6. Preheat the oven to 350 degrees F. Bake the cookies for 15-18 minutes until lightly golden around the edges, increasing or decreasing the baking time as needed. Let the cookies sit on the baking sheets for 2-3 minutes after removing from the oven before sliding to a cooling rack to cool completely. 7. The shortbread can be stored covered at room temperature for several days.