Preheat oven to 350 degrees F. Line two cookie sheets with parchment paper and set aside.
To a large mixing bowl, add the cake mix and baking powder. Stir to combine.
Mix the eggs, oil, milk, and vanilla into the dry ingredients. Then fold in M&Ms and chocolate chips until combined.
Scoop out balls of dough using a 1.5 tablespoon cookie scoop. Do not flatten as they will spread. Ensure to leave some space in between each ball. Add a few extra M&Ms and chocolate chips on top, if desired.
Place the cookie sheet in the freezer for 5 minutes prior to baking. If you are working in batches, you can store the rest of the dough in the fridge until ready to scoop.
Bake for 9 minutes to keep the cookies chewy. Remove from the oven and let cool on the cookie sheet for 2 minutes before transferring to a wire rack to cool completely.