Heat butter in microwave until ¾ of the way melted, about 30 seconds. Set aside.

In a medium bowl sift together flour, cocoa powder baking soda, baking powder, and salt. Set aside.

In a small bowl whisk together egg, egg yolk, and vanilla.

Using an electric (stand or handheld) mixer cream together butter and brown sugar until combined. Add egg-vanilla mixture until combined.

Slowly add in dry ingredients until just combined. Gently fold in chocolate chips. Refrigerate dough for at least 30 minutes.

Once dough is cooled, preheat oven to 350 degrees and line a cookie sheet with parchment paper. Form balls of dough with 3-4 tablespoons of dough each and arrange on cookie sheet. Bake until centers just start to set, about 10 minutes. Let cool on baking sheet for 5 minutes. Transfer to a wire rack to cool completely. Enjoy!