Line baking sheets with parchment paper and set aside.
To the bowl of a stand mixer, add butter and sugar and beat on MED speed until smooth and well combined. Mix in the eggs, one at a time, until combined. Add vanilla and mix.
To a mixing bowl, add dry ingredients (flour, cornstarch and salt), and whisk to combine. Add the flour mixture, starting with 3 cups, and mix on MED LOW speed.
Let mix for 3-5 minutes, and you'll see the dough go from a crumbly mess to pulling itself into a ball that pulls away from the sides of the mixer bowl.
Turn out the dough onto work surface and roll dough to a thickness of about 1/4 inch. Flouring the work surface and rolling pin is helpful, as is rolling dough out between 2 pieces of wax or parchment paper.
Cut into shapes and place cut out dough pieces on prepared baking sheets. Refrigerate for 15 minutes.
While dough is chilling, preheat oven to 375 F degrees.
Bake cookies for 9-11 minutes, or until edges appear set. Cookies won't be golden on the top.
Remove from oven and let cookies sit on baking sheet for 2-3 minutes, then transfer to a wire cooling rack and cool completely.
Decorate if desired.