Preheat oven to 350° F.
In an electric mixer cream together butter and sugar until well combined and creamy. Add in egg and vanilla extract and beat until everything is fully incorporated.
Mix in cocoa powder, baking powder, salt, cinnamon, and flour until it forms a batter. Pour in melted chocolate and stir until well combined.
Scoop dough, form into balls and place onto a lined baking sheet. Bake for 8 minutes or until cookies are just dry on top. Be careful not to overbake.
Remove tray from oven and leave cookies on baking tray to cool completely.
Once cookies are completely cool prepare icing. In a saucepan melt butter. Add remaining ingredients, whisking until smooth and pourable. If mixture is too thick add more milk 1 teaspoon at a time to get to a pourable consistency.
Pour frosting over cooled cookies on baking tray. Let cookies sit for a couple of hours for icing to completely set.
Remove and store in an airtight container for up to 3 days.
