Preheat the oven to 350 degrees and line cookie sheets with parchment paper or silicone mats.
In a medium mixing bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.
In a large mixing bowl (hand mixer or stand mixer with the paddle attachment), beat together the butter and sugar until light in yellow and fluffy in appearance.
Add in the egg, red food coloring*, vanilla extract, and white vinegar and beat together on medium speed until combined.
Slowly add in the dry ingredients, about 1 cup at a time. Mix on low speed in between each addition.
Once all of the dry ingredients have been incorporated, the mixture will be slightly dry (if it’s not, then stop here). Add 1 tablespoon of buttermilk in and mix on high for 10-15 seconds to bring together the dough. Add another tablespoon if needed. As soon as the dough no longer is crumbly, stop mixing.
Roll out dough to ⅜” inch* between two sheets of wax paper.
Create your shapes with your cookie cutters and place them on the prepared cookie sheet.
Bake for 10-12 minutes until the top of the cookies no longer looks shiny and raw, but solid with a matte texture.
Remove from the oven and allow the cookies to cool for about 5 minutes so the shapes set. Transfer to a wire rack to cool completely.
Decorate with royal icing or your desired frosting!