In a big mixing bowl, add the flour, cornstarch, and kosher salt. Mix with a whisk until combined and set aside.
Into a big mixing bowl, or in a bowl of a stand mixer, add the room temperature butter and the powder sugar, and cream it for 2-3 minutes or until it’s creamy and light in color.
Add the eggs, and vanilla extract. Cream the butter until the mixture is creamy and light.
Add half of the dry ingredients and mix until almost combined. Add the other half of the dry ingredients. Mix until the mixture is just combined and you cant see pockets of flour.
Cover the Christmas sugar cookies dough with plastic wrap and let the dough rest in the fridge for at least an hour. We let the dough rest in the fridge overnight but it’s not a must.
After letting the dough chill in the fridge for at least an hour, take one dough half out of the fridge. Start rolling the dough on a floured clean surface to about ¼ inch thick.
Using cookie cutters, cut as many cookies as you can, we use a Christmas tree one, heart shape, star, and a circle but you can use your favorite cookie cutters as well. Carefully transfer the cookies onto a parchment paper-lined baking sheet and bake in a 180c (350f) preheated oven for 10 minutes or until the edges are starting to turn golden.
Take the cookies out of the oven and let them cool for 10 minutes. Then transfer them to a wire rack to cool completely.