In a large mixing bowl, add the butter and sugar and beat for 1 minute until fluffy.
Add the egg and vanilla and mix until blended.
Add the dry ingredients (flour, cocoa powder, and baking powder) into the wet ingredients and mix until flour is incorporated.
Add in the chocolate chips and m&ms and gently stir them in.
Place in the refrigerator for 30 minutes to chill.
Preheat your oven to 350° F.
Line baking sheets with parchment paper.
After dough has chilled, use a cookie scoop to scoop onto baking sheet 2 inches apart.
Bake for 12-14 minutes.
Remove from oven and let cool on baking sheet for 5 minutes
Cool completely and then store in an airtight container for up to 4-5 days. Use brown sugar instead of white sugar if preferred.I love dark chocolate chips but use milk chocolate or semi-sweet chocolate chips if preferred.Substitute Reese's pieces for the m&ms.Add chopped pecans or chopped walnuts if desired.