Melt the chocolate au bain marie in a heat-resistant bowl. Make sure the bowl doesn't hit the water. As soon as it is melted, leave to cool.
Whisk the cream together with the cinnamon till you have soft peaks. You can add a bit of sugar if you want. Depending on how sweet you want the chocolate mousse to be.
Once the chocolate is luke warm fold the whipped cream through the chocolate until you have a smooth and even colored mousse.
Using a piping bag add to serving glasses and place in the fridge until ready to use.
Notes
Storing: You best make this mousse 2-3 hours before ready to serve. You can also store it in the fridge for up to 2 days.