Beat together butter, sugar, brown sugar, eggs and vanilla in either a stand up mixer (using the flat beater attachment) or a hand mixer. (The wet ingredients.) * You will want to ensure the ingredients are well incorporated and are smooth.
Mix the flour, coco powder, baking soda and salt. (The dry ingredients.)
Add the dry ingredients to the wet ingredients.
Once the dry ingredients are incorporated into the wet ingredients, add the M&M and chocolate chips combination to your batter by hand.
Line two baking sheets with parchment paper or a silicone mat.
Scoop dough into balls that about about 2 - 3 teaspoons in size. Than place the dough balls evenly spaced on the baking sheets.
Place the M&M's that were set aside on top of each cookie for decoration.
Place the cookies into an oven that has been preheated to 350 degrees for 10 - 12 minutes. The time can vary depending on your oven and your personal taste.
This batch should yield 3 dozen cookies, but that can vary depending on the size of cookie balls.