Tangerine mousse With rhubarb sauce

For the sauce

1. Boil the 375g rhubarb with the sugar and water for 5 minutes, skim and pass.
2. Discard the pulp. Add the scraped vanilla pod to the syrup and bring back to the boil.  Add the trimmed lengths and poach for 1 minute – leave to cool, then chill.

For the mousse

1. Heat the tangerine juice with half the zest until it reduces to 30-40ml. In another pan bring the water and sugar to the boil to dissolve and add the juice mixture. It should have a consistency of marmalade.
2. Bring the egg yolks to a light and fluffy state over hot water, continue to beat and add (slowly) the juice mixture. Remove from the heat and continue beating till cold with a hand whisk. Whip the cream to soft peaks and fold into the egg mixture.  Fold the other half of the zest into the mixture. Pour into 6 ramekins or suchlike and freeze for 6 hours. 
3. To serve, divide the sauce between 6 soup plates and dip each of the moulds in very hot water and set in the middle of each. Dust with icing sugar and serve.