Put the cocoa powder (if you are using real cocoa, add more sugar) with the cinnamon sugar (or normal sugar, but then add more cinnamon) and the cinnamon in a cup, then mix with the milk. A thick sentence should emerge.
When the cocoa is mixed without lumps, simply add a cup of coffee. If possible, the coffee should be a little stronger than if you were drinking it black or with only milk and / or sugar.