- On a plate, scatter the grated orange zest. Cook in the microwave oven for 30 seconds at a time, stirring between each stop, until the zest is completely dry, about 2 to 3 minutes (Careful, the zest can burn quickly). With a mortar, grind the zest into a fine powder with the sugar. Set aside.
- In a small saucepan off the heat, whisk the milk and cocoa powder. Add the cinnamon stick and large big orange zest. Bring to a boil, whisking constantly. Simmer over low heat for about 5 minutes, whisking constantly. Add the chopped chocolate and simmer for 1 minute. Off the heat, remove the cinnamon stick and zest. Keep warm.
- With a milk frother, froth the milk until it is warm and makes a nice foam.
- Pour the hot chocolate into cups. Top with the milk froth. Sprinkle with a little orange powder.