Beat the eggs and sugar together in a bowl. Now place the bowl over a pan of simmering water and continue to whisk. This will cook the eggs gently add the mixture will lose the ‘eggy’ flavour.
Transfer the mixture to a clean bowl and beat well until it doubles in volume. Add the lemon zest and vanilla extract and mix thoroughly. Set to one side to cool.
When the mixture has cooled, add the mascarpone, crème fraiche and whipped cream. Mix gently and transfer to lightly greased individual moulds. Cover with cling film and chill in the fridge for approximately 2-3 hours, until set. To serve the mousse, place the moulds in a basin of warm water for 30 seconds. Then turn them upside down onto your serving plate and the moulds should come away easily. Be gentle.
Wash the rhubarb, dry and cut into lengths 3-4 cm/1¼ – 1½ inches long.
Place the sugar and water in a large shallow pan, bring to the boil and dissolve the sugar.
Add the rhubarb stalks and cardamom seeds. Poach gently for 3-4 minutes. Do not overcook. Serve warm or cold.