In a medium bowl, mix the flour, cocoa powder, baking soda, and salt. Set aside.
2 cups All-purpose flour, 1/2 cup Unsweetened cocoa powder, 1 tsp Baking soda, 1 tsp Salt
Using a mixer, beat the butter, brown sugar, and sugar on high speed for 2 minutes.
1 cup Unsalted butter, 1/2 cup White granulated sugar, 1 cup Brown sugar
Add in the vanilla, egg, and egg yolk. Beat on medium speed until combined. Make sure to scrape the sides of the bowl using a rubber spatula.
1 tsp Pure vanilla extract, 1 Large egg, 1 Egg yolk
Add in the dry ingredients and mix on low speed until just combined. Add in the chocolate chips. This will be a thick dough.
1 1/2 cups Semi-sweet chocolate chips
Preheat the oven to 350℉. Line two cookie sheets with parchment paper. Let the cookie dough sit for 10 minutes before scooping.
Using a large cookie scoop (2 oz or 2 Tablespoons) to scoop the cookie dough. Place 6 cookie dough balls per cookie sheet.
Bake for 13-15 minutes. Let the cookies sit on the hot pan before transferring to a cooling rack. Cool the cookies completely before decorating.