Preheat your oven to 180°C (gas mark 6)
For the biscuit :
Whisk 3 egg yolks with 75g sugar and the vanilla sugar in a bowl. Add the sifted flour and milk. Gently fold in 3 stiffly beaten egg whites. Pour the mixture into a buttered 26 cm cake tin. Bake for 35 minutes. Turn out onto a wire rack and leave to cool.
For the mousse:
Soak the gelatine in water for 5 minutes, grate the mandarin zest and squeeze out the juice. Squeeze out the gelatine and melt in the hot mandarin juice. Melt the chocolate with a little water and mix with the mandarin juice and the 2 tablespoons of Ælred mandarin liqueur. Add the butter, cut into small pieces. In another bowl, whisk 3 egg yolks with the remaining sugar and add the chocolate mixture. Fold in the 3 stiffly beaten egg whites. Chill for 2 hours. Cut the biscuit lengthways into 4 slices. Line the cake tin with cling film. Fill with alternating layers of biscuit and mousse, starting and ending with the biscuit. Close the cling film and chill in the fridge for 12 hours. Enjoy!
