In a bowl, mix together flour, cocoa powder, and baking soda. Set aside
In a separate bowl, mix together the egg and brown sugar
Add in the melted butter and melted chocolate
Mix in the dry ingredients until well combined
Scoop out the batter onto a baking sheet
Place on the mini Oreos and M&Ms
Bake at 180C/356F for 10 minutes
Allow cookies to cool before doing final decorations with royal icing.