Preheat oven to 200 degrees C. Grease a 23cm springform cake tin.
Whisk three egg yolks with warm water until fluffy. Add 2/3 of the sugar and the vanilla. Whisk the egg whites with the remaining sugar until stiff and fold into the yolk mixture. Stir in flour and baking powder.
Pour mixture into the prepared springform tin and bake for 15 minutes until a skewer comes out clean.
For the filling, stir the creme fraiche along with the egg yolks, sugar, vanilla and lemon juice until smooth. Beat egg whites until stiff and fold in.
Dissolve the gelatine according to packet instructions in water, heat and stir into the creme fraiche mixture.
Allow the cake to cool and then cut through it in half to make two rounds.
Line the springform tin with plastic wrap. Lay the cake with the cut side up in the springform tin. Spread the creme fraiche mixture over the pastry and smooth out.
Cut the top piece of pastry into 12 or 16 wedges and lay on top of the creme fraiche mixture.
Chill until the mixture is set. Dust it with icing sugar to serve.