In a large bowl, cream together the butter and sugars until light and fluffy.
Beat in the egg and vanilla and continue mixing until combined. Scrape down the sides of the bowl as needed.
In a separate medium bowl, add the flour, cocoa powder, and salt and mix.
Add the dry ingredients into the wet ingredients, slowly. The dough will be thick.
Using a spoon, mix in the milk then fold in the chocolate chips.
To make the peanut butter cookie dough
In a large bowl, cream together the butter and sugars until light and fluffy.
Beat in the peanut butter, then the egg, and then the vanilla (in that order). Scrape down the sides of the bowl as needed.
Mix in the baking soda and flour until just combined.
Fold in the chocolate chips.
Chill both doughs for at least 1-2 hours. I did mine overnight.
Preheat the oven to 350 degrees and line a baking sheet with a silicone baking mat and set aside.
Using a cookie scoop (it's best to use 2 cookie scoops - one for each dough), scoop one chocolate and one peanut butter. Roll each dough into balls them smush them together and roll into a large ball. I did 8 per pan since they're pretty large.
Bake the cookies for 11-12 minutes. The cookies will look soft and underdone, but they will continue to cook on the pan after you take them out.
After about 5 minutes, transfer the cookies to a wire rack to finish cooling.