Preheat the oven to 375 F/190 C.
In a medium bowl, combine the flour, salt, corn starch and baking powder and set aside.
3 cups all-purpose flour, 2 tablespoon corn starch, ¼ teaspoon kosher salt, ¼ teaspoon baking powder
In a stand mixing bowl, add the room temperature butter and sugar. Mix with the paddle attachment on low until JUST combined. Don't cream them together or the cookies will spread!
8 ounces unsalted butter, room temperature, 1 ½ cups granulated sugar
Stop the mixer and scrape down the bowl with a rubber spatula. Add in the egg and vanilla and mix on low until combined.
1 large egg, room temperature, 1 teaspoon vanilla extract or vanilla bean paste
Add the bowl of dry ingredients and mix on low until the dough starts to come together. When there are no more large pockets of flour, stop mixing.
Grab half of the dough from the bowl and place it on top of a piece of parchment paper. Place a second sheet of parchment paper on top and press the dough down into a flat disk. Use a rolling pin to roll the dough into your desired thickness and then transfer the slab to a baking pan. Place the pan in the freezer while you roll out the other half of the dough the same way.
Leave both slabs of dough in the freezer for 5-10 minutes or until the dough is cold and firm. Remove the top sheet of parchment and use your desired cookie cutter to cut out the cookies. You can rework the dough twice, but no more than that or the cookies will shrink and be tough.
Place the cut out cookies on a lined baking tray and place them in the freezer until frozen solid, anywhere from 10-20 minutes.
Bake the cookies on a lined tray space 2 inches apart for 10-13 minutes depending on the size and thickness, or until the tops look matte, dry, and slightly wrinkled. Do not let the cookies brown on the edges or they will be crisp and not chewy!
Allow the tray to cool completely on a wire rack before removing and decorating them.