Sift together the flour, corn starch, cocoa powder, and salt into a large bowl. Whisk these dry ingredients until evenly combined.

In another bowl, beat the butter and sugar together using a mixer on medium-low speed with a paddle attachment until well mixed.

Add the egg and vanilla to the butter mixture and continue mixing, making sure to scrape the sides of the bowl to combine everything.

Gradually add the dry flour mixture to the wet ingredients. Mix on low speed for about 30 seconds until the dough forms and sticks to the paddle.

Roll out the dough between two pieces of parchment paper. Place the rolled dough on a baking sheet and refrigerate for 1 hour.

Preheat your oven to 350 degrees F. Once the dough is chilled, use cookie cutters to cut out shapes.

Bake the cookies for 8-12 minutes until the centers are set. Allow them to cool completely on a wire rack.