1/2cup(8 tablespoons) unsalted butter, room temperature
1/2cuppacked dark brown sugar
1teaspoonpure vanilla extract
3/4cupDutch processed cocoa powder
In a large mixing bowl, cream together the butter, sugars and vanilla until light and fluffy, about 2 minutes. Meanwhile, in a separate medium bowl, whisk together the flour, cocoa powder, baking soda and salt.
Combine the dry ingredients to the butter mixture and stir until incorporated. Pour in the milk and mix until just combined.
Transfer the dough to a clean workspace and form into two 1+1/2-inch logs. Wrap tightly with plastic wrap and refrigerate for at least 1 hour.
When ready to bake, preheat the oven to 350 degrees F and line two baking sheets with parchment paper or silicone mat. Use a serrated knife to slice the cookie dough into 1/8-inch discs, working with one log at a time and keeping the other in the fridge until ready to slice and bake. Place the discs on the prepared baking sheets.
Bake for 8 minutes, rotating the pans halfway through. Allow the cookies to cool on the pans for 5 minutes before transferring to a wire rack to cool completely.