Preheat your oven to fan 160c, conventional 180c and gas 4. Grease and line two 7inch/17.5cm sandwich tins. Then, finely chop all the dark chocolate.
Sift the flour and baking powder into a bowl than add the suger. Make a well in the centre and add the butter, milk and eggs. Beat together with an electric whisk for two minuites or 3 minuites with a wooden spoon.
Take the orange and squeeze the juice into the mixture and lightly fold in the chopped chocolate.
Evenly divide the mixture between the two tins and flatten it with a spatula. Cook the mixture for 25 to 30 minuites or until it springs back when you touch it. When you insert a skewer it should come out clean.
Take out of the oven, leave for 5 minuites then turn out onto a wire rack leave to cool for one hour.
Wilst the cakes are cooling break up the white chocolate into a pan and melt it (be careful not to burn it) then leave it for 5 minuites. Peel the satsuma and break it into it segments dip them into the white chocolate and put them into the fridge to set.
Add the creme fraiche to the chocolate and squeeze the orange's juice into the mixture. Mix until it's smooth and shiny then leave for five minuites. Then put half the mixture into a seperate bowl and add the orange rind.
To put it together take one of the cakes and put it on a plate so the bottom's facing the sky. Add the creme fraiche mixture with orange rind and smooth it with a spatula. Add the other cake on top of it than spread the other mixture evently on it with a spatula. Finally, take the satsuma segments and place them evenly on the top of the cake