Step 2: Making the shortbread
Preheat oven to 300oF (150C) and place rack in center of oven.
With an electric mixer or hand mixer, beat the butter and sugar until light and fluffy.
Add egg and beat until combined.
Beat in the vanilla extract.
Add the flour and salt and beat until the dough just comes together.
Refrigerate the dough until firm.
Roll out the dough or press onto a baking sheet lined with parchment paper.
Bake for 20 - 30 minutes, turning the baking sheet front-to-back half-way through baking.