Cream the butter and sugars together with a handheld or stand mixer fitted with a paddle attachment on medium-high speed until light and fluffy, about 3 minutes. (Here’s a helpful tutorial if you need guidance on how to cream butter and sugar.) Add the egg and vanilla extract, and then beat on high speed until combined. Scrape down the sides and up the bottom of the bowl as needed. In a separate bowl, whisk the flour, cocoa powder, baking soda, and salt together. With the mixer running on low speed, slowly pour into the wet ingredients. Beat on low until combined. Switch to high speed and beat in the milk, then the chocolate chips. The cookie dough will be sticky and tacky.

Cream the butter and sugars together with a handheld or stand mixer fitted with a paddle attachment on medium-high speed until light and fluffy, about 3 minutes. Add the egg and beat on high speed until combined. Scrape down the sides and up the bottom of the bowl as needed. Add the peanut butter and vanilla extract and beat until combined. With the mixer running on low speed, slowly add the flour, baking soda, and salt. Once combined, beat in the chocolate chips.

Cover both cookie doughs tightly and chill in the refrigerator for at least 3 hours or up to 3 days. It’s imperative that both doughs are chilled, otherwise the doughs will be difficult to work with, and the cookies will overspread.

Preheat oven to 350°F (177°C). Line large baking sheets with parchment paper or silicone baking mats. (Always recommended for cookies.) Set aside.

Measure about 2 Tablespoons (40g)—or a little less, because the recipe makes *slightly* more peanut butter dough—of chocolate cookie dough. Roll into a ball. Measure about 2 Tablespoons (40g) of peanut butter cookie dough. Roll into a ball. Press the 2 balls together between your hands and roll them into 1 large ball. Repeat for each cookie. The chocolate cookie dough is particularly sticky, so wipe your hands clean after every few balls of dough you shape.

Bake the cookies for 12–14 minutes or until the edges appear set and the centers still look soft. Tip: If they aren’t really spreading by minute 9, remove them from the oven and lightly bang the baking sheet on the counter 2–3x. This helps initiate that spread. Return to the oven to continue baking.

Cool cookies for 5 minutes on the baking sheet. During this time, I like to press a few more chocolate chips into the tops of the warm cookies. (This is optional and only for looks.) Transfer to wire rack to cool completely. The cookies will slightly deflate as they cool.

Cover leftover cookies tightly and store at room temperature for up to 1 week.