Preheat oven to 350 degrees.
Line baking sheet with parchment paper or ungreased baking sheet.
Using mixer, beat together the butter and sugars until well combined.
Beat in the egg and vanilla until just combined.
Add the flour, cocoa powder, baking soda, and salt and beat until a soft dough forms.
Stir in the milk chocolate chips and Nutella M&Ms.
Using a medium scoop, heaping 1 ½ tablespoons, scoop the dough and continue to roll into balls. Gently press some extra chips and m&m’s on top of cookies, if desired.
Place cookie balls on cookie sheet and bake for 12 minutes exactly. Cookies will look slightly underdone, but will firm up as they cool. If making smaller cookies, reduce time; if making larger cookies increase time by a few minutes.
Cool for 5 minutes on the pan before removing to a cooling rack.