Combine the frozen cranberries with the water, cinnamon, and vanilla pods and seeds in a sauce pot. Bring to a boil. Crush the cranberries as they are cooking to release the moisture in them.
Once all of the cranberries have burst and the liquid has boiled for about 5 minutes, pass the liquid through a fine-mesh sieve.
Stir in the sugar until it has dissolved. Adjust the sweetness if necessary. There should be about 600g/1lb5.12oz of cranberry juice.
Using a handheld blender, blend the egg white powder in, and then the xanthan gum. Using an immersion blender, mix for about 5 minutes in a deep stainless-steel cylinder, since it will foam and increase in volume as it is mixed.
Reserve in the refrigerator for 2 hours before service. The froth will accumulate on the top; this is what you will be spooning onto the mousse during service.