Place rhubarb, sugar and vanilla into the Thermomix bowl and cook 25 min/90°C/speed soft. it will be noisy in the beginning, but as it cooks it quietens down.
Check for doneness, the mixture should be quite liquid and fragrant. If it needs more cooking time, add 5 minutes.
Scrape out of the Thermomix bowl into a plastic container and chill in the fridge until completely cold. This is quite a dark mixture at this stage, but never fear. The churner is here!
Before churning, return the mixture to the Thermomix bowl and add the egg white and coconut cream. Blend *10 sec/speed 10.
Churn according to manufacturer's instructions. Store in a container of choice until use.
Thermomix method; After adding the egg white and coconut cream, freeze in a flat tray until totally solid.
When ready to serve, cut into chunks and fill the Thermomix bowl to about the half way mark. Blend 10 sec/speed 10. Add the rest of the frozen mixture and continue to blend with the aid of the Thermomix spatula, 1 min/speed 9. Serve immediately or store as above.