Break the chocolate into small pieces and place in a bowl with the butter and half the caster sugar over a pot of simmering water, leave until everything is melted, and then stir until all ingredients are combined.
Put the eggs and the remaining sugar into a large bowl and whisk until the mixture has doubled in size and be very thick and pale.
Transfer to a large bowl and gradually fold in the flour and then the cooled melted chocolate mixture (if the mixture 'splits' at this point, add a little water and it will emulsify again).
When ready the mixture will be quite runny, at this point, pour it into a grease and line 9inch springform cake tin (with a removable base) and bake in the oven for 6 minutes, the rim will be cooked while the centre appears liquid.
Leave the cake to cool and cover and leave in a cool place (not the fridge) It is best to leave this cake set overnight.
For the ganache topping soak the cranberries in the Cointreau. Grate the rind and juice the orange and add to the cranberries.
Chop the chocolate into small pieces. In a saucepan bring the cream to the boil. Pour over the chocolate. Leave to stand for 5 minutes then whisk until all the pieces are melted together. Stir in the cranberries. When cold cover and leave in the fridge over night.
Whisk until very thick and spread on top of the dark chocolate ganache cake.
Now place in the freezer 4 hours to firm it up for the glaze.
For the ganache glaze chop up the chocolate into small pieces, put in a heat proof bowl, add all remaining ingredients.
Place the bowl over a simmering saucepan of water, stir until melted.
Dip a sharp knife into hot water then run around the frozen cake.
Place a wire cooling rack over a tray. Put the cake on top then pour the glaze over.
Allow all the excess chocolate to drip off the place on a plate or a cake board. Decorate with chocolate shavings.