Simple Scottish Shortbread

Favorite cookies from Scotland that will melt in your mouth. Delicious for tea!
Whisk together the butter, powdered sugar and vanilla until smooth. Add the flour, one cup at a time, to the butter mixture.On a floured surface, roll out the dough 1/4 to 1/2 inch thick. Using a sharp knife, cut the dough into 2-inch-thick squares or cut into 1 3/4-inch-thick circles using a cookie cutter.Place on a greased baking sheet and prick the top of the cookies with a fork. Bake at 325 degrees for 20 minutes or until the cakes are golden and the tops are light. Cool on wire racks. Store in an airtight container.