Preheat the oven to 350 F.
In the bowl of an electric mixer, combine the butter and sugar. Beat on medium-high speed until light and fluffy, about 2-3 minutes.
Blend in the eggs one at a time, scraping down the bowl as needed, then mix in the dark cocoa powder until well blended.
Add the all-purpose flour, .coarse saltregular salt can be used, and .baking powder to the bowl and mix on low speed just until incorporated.
Fold in the Holiday M&Ms and chocolate chips with a spatula.
If the dough is thick, stir with the spatula until just combined.
Using a standard size cookie scoop, portion the dough onto cookie sheets. To make 36 cookies, place about 12 cookies on each sheet.
Bake for approx 10 minutes. Let the cookies cool on the cookie sheets for 5-10 minutes, then transfer to a wire rack to cool completely. Store cooled cookies in an airtight container.