01 -
Line 2 baking sheets with parchment paper or silicone baking mats.
02 -
In the bowl of an electric mixer, combine the butter and sugars. Beat together on medium-high speed for 2-3 minutes until light and fluffy. Blend in the egg and vanilla extract, scraping down the bowl as needed.
03 -
In a separate bowl, whisk together the flour, cocoa powder, baking soda, and salt.
04 -
Slowly add the dry mixture to the wet ingredients in the mixer at low speed until just incorporated.
05 -
Mix in the milk on the lowest speed, then fold in the chocolate chips.
06 -
Preheat the oven to 350˚F.
07 -
Roll about 2 tablespoons of dough into balls and place them on the prepared baking sheets. Press down slightly if you prefer thinner cookies.
08 -
Top the dough balls with M&M's and place the baking sheet in the freezer for 10-15 minutes. Alternatively, chill the dough for at least 1 hour or up to 36 hours.
09 -
Bake the cookies for 10-11 minutes. Immediately top with more M&M's if needed.
10 -
Let the cookies cool on the baking sheets for about 5 minutes, then transfer them to a wire rack to cool completely.