Heat the oven to 160C/140C fan/gas 3. Grease and base line a 1 litre heatproof glass pudding basin and a 450g loaf tin with baking parchment.
Put the butter and chocolate into a saucepan and melt over a low heat, stirring. When the chocolate has all melted remove from the heat.
In a large bowl mix together the flour, baking powder, bicarbonate of soda and muscovado sugar. In another bowl beat together the eggs, soured cream and vanilla extract. Pour the egg and chocolate mixtures into the flour and mix thoroughly together.
Weigh 250g into the loaf tin, then spoon the rest of the mixture into the pudding basin.
Cook both cakes side by side in the oven. The loaf cake will cook in about 30 mins and the basin cake in about 1 hour. Take the loaf cake out of the oven and close the oven door quickly so as not to allow the heat out. Test with a skewer inserted into the centre, it should come out clean. If not return to the oven for another five mins. Repeat with the basin cake after about another half an hour. Once each cake is cooked, allow to cool completely before turning out.
To make the icing, mix together the cocoa and water to make a smooth paste. Beat the butter until soft and gradually beat in the icing sugar. Add the cocoa paste and beat until smooth.
To assemble the cake, trim the top of the basin cake so it is flat. Turn cut side down onto a board and cut in half vertically. Spread a little butter icing on each of the flat bases and sandwich these two buttercreamed surfaces together to make a rugby ball shape for the hedgehog body. Place onto a 30cm cake board or wooden board. Cut the loaf cake in half vertically. Take one half and trim the short end to a v shape to make the pointy head. Use a little icing to attach to the body. Cut pieces from the remaining loaf cake to fill any gaps. Cover the whole cake in butter icing.
Cut the flake bars into pieces ranging from 2.5cm to 5cm. The spikes do not have to be regular or even in shape. Starting at the front push the spikes into the body of the hedgehog at a slight angle. Start with the small pieces gradually using larger ones as you go towards the back. Press a round chocolate into the tip of the head to
represent the nose and use chocolate chips for the eyes. Using a tiny bit of butter icing attach sliver or gold balls to the eyes.
The cake is best made the day before cutting and icing and will keep well for 3–4 days.