Start by making the double chocolate cookie dough. Cream the butter and sugars together with a mixer (stand or hand) on medium speed until light and fluffy. Beat in the egg and vanilla until combined. Add in the flour, cocoa powder, baking soda, and salt. Slowly mix it all together until combined. Add the milk and mix until it is just combined. The dough will be sticky. Stir in the chocolate chips.
Make the peanut butter dough. Cream the butter and sugars together with a mixer (stand or hand) on medium speed until light and fluffy. Mix in the peanut butter, egg, and vanilla. Slowly mix in the baking soda and flour. Try not to overmix. Stir in the chocolate chips.
Chill both the chocolate and peanut butter dough for at least 1-2 hours. If you are in a hurry, throw it in the freezer for about 45 minutes to an hour. It’s important to chill the dough or the chocolate dough will be so sticky that it will prove to be nearly impossible to roll it into balls without it getting everywhere.
Preheat oven to 350F degrees. With a cookie scoop or spoon, scoop about a 1 – 1/2″ ball of peanut butter dough. Roll into an even ball. Take the same size scoop of chocolate cookie dough. Roll into a ball. Smoosh the two balls together and roll them into 1 large ball. Repeat for each cookie. The chocolate cookie dough will be sticky.
Bake the cookies for 11-12 minutes. The cookies will look very soft, puffy, and almost undone. Allow the cookies to cool on the cookie sheet and they will continue to “bake” and set up. As they cool, the cookies will firm up.
Notes
It's important to CHILL both the chocolate and peanut butter dough for at least 1-2 hours. This will allow the dough to be easier to roll.Do not overbake the cookies. These should be taken out of the oven when soft and puffy.