Whisked together flour, cocoa powder, baking soda, and salt. Once combined set aside.
Using a stand mixer or electric mixer beat softened butter with melted chocolate, sugar, and brown sugar. Once well combined add in egg, vanilla extract, and milk. Add in dry ingredients and mix until well combined.
Fold in 1 cup Christmas M&Ms. Place dough in the fridge and allow to chill for at least 2 hours.
Pre heat oven to 350 degrees F. Prepare a baking sheet with parchment paper and roll out into 1 inch balls and place them on your baking sheet. Add remains 1/4 cup Christmas M&Ms to the tops of each cookie. Bake for 12-13 minutes.