Cream the butter and sugars together with a hand or stand mixer on medium speed until light and fluffy. Scrape down the sides and bottom as needed. Beat in the egg, vanilla, and milk until combined. In a separate bowl, combine the flour, cocoa powder, baking soda, and salt. Slowly mix into the wet ingredients. Fold in the baking morsels. Transfer dough to a bowl, cover with plastic wrap and refrigerate immediately.
Peanut Butter Cookie Dough:
Cream the butter and sugars together with a hand or stand mixer on medium speed until light and fluffy. Scrape down the sides and bottom as needed. Mix in the peanut butter, egg, and vanilla. In a separate bowl, combine the flour, baking soda, and salt. Slowly mix into wet ingredients. Fold in baking morsels. Transfer dough to a bowl, cover with plastic wrap and refrigerate immediately.
Cookie Instructions:
CHILL both doughs for 2 hours; may alternately chill in the freezer for 45 minutes, if in a hurry.
Preheat oven to 350 degrees Fahrenheit. Line cookie sheets with silicone baking mats or parchment paper. Using a #50 cookie scoop (about 1½ Tbsp) scoop all the peanut butter cookie dough onto prepared baking sheets (almost 3 dozen cookies - so 3 baking sheets with a dozen on each tray). Clean scoop and repeat with the chocolate cookie dough placing it directly next to the peanut butter dough balls.
Grease hands with baking spray, press both doughs together, and roll them into 1 large ball. Repeat for each cookie. Press extra baking morsels into the tops of each cookie (optional).
Bake at 350 degrees Fahrenheit for 11 to 12 minutes; they will be soft, puffy, and look barely baked through. Allow cookies to rest on the tray for several minutes before transferring to a wire rack to cool. Store in an air tight container; cookies stay fresh (and soft) for up to 10 days.