In a large bowl of an electric mixer, beat butter and brown sugar on medium speed for 1-2 minutes. Then add the milk, vanilla, and salt. Beat to combine.
In a small bowl sift flour and cocoa powder. Meanwhile melt 2 oz chocolate in the microwave.
Add the dry ingredients to the butter and sugar mixture. Beat on low speed until incorporated, then add the 2 oz melted chocolate. Once fully incorporated, add the mini chocolate chips and mini M and M’s. Refrigerate until firm but pliable, approximately 1 hour.
Once chilled, form cookie dough into 1-inch round balls and place on a parchment lined baking sheet. Freeze for 15-30 minutes.
Dip each ball into the melted chocolate and coat to cover. Sprinkle with extra mini chocolate chips and refrigerate. When the chocolate has hardened, they are ready to be served!
Keep in the refrigerator for 1-2 weeks. They also keep very well frozen.