Add the cocoa powder, sugar, and cinnamon to a small saucepan. Add a splash of the milk and whisk (no heat yet) until fully combined. It will go through stages from very powdery, to somewhat mixed, and then will suddenly come together completely.
Once completely mixed, slowly add the rest of the milk to the mixture while whisking.
Using the back of your knife, give the ginger "coins" a few good smacks to get the juice flowing. Add them to the saucepan.
Heat the mixture over medium heat, whisking occasionally, until scalded but not quite boiling (bubbles will form around the edges, but will not be a full boil).
Remove from heat. Pour into glasses, discarding the ginger. Top with dairy free whip or marshmallows!
I often make a double batch and store it in the fridge for later. It's great cold, and can also be reheated easily. Perfect for a snowy week!