Mix the milk with sugar and egg yolks. Stir in the gelatin and continuing mixing in a bain-marrie on medium heat, until the mixture reaches the consistency of a thick cream.
Allow the mixture to cool completely and mix it with whipped cream,vanilla,orange zest and orange peel .
Peel oranges, cut oranges into thin slices and line a 25 cm diameter baking tray. Pour half of the cream over the oranges, then place on top a layer of butter rich biscuits and the chopped orange.
Mix the other half of the cream with the cocoa and pour over the biscuits, then cover with another layer of biscuits.
Allow to cool for 4 hours then put a plate over the baking tray and invert the cake in one go,so that the oranges are now forming the top of the cake.