Beat the butter till light and fluffy. Meanwhile melt the chocolate and let it cool a little. Gradually add the sifted icing sugar and the cocoa powder and then the chocolate and vanilla and beat till light. Chill a little so it is easy to spread.( can be made ahead then brought back to room temperature)
Fill each layer of the cake with about 1 cup of icing, leaving an equal amount to cover the cake.
Start by adding a large amount onto the top of the cake and start spreading it right across the top and down the sides. It will take a while to get the frosting even and completely covering the cake in a nice thin layer as smooth as possible. The cake only needs a fine coating. Chill to set.
Knead the black icing till smooth. Sprinkle a small amount of icing sugar onto a bench with a sifter and brush till it is very well spread and thin. The sugar will make the black icing look white if you use too much. To make a cake of this size you will need to roll out approximately a 15 in / 38 cm diameter icing. As you roll run the pallet knife under the black icing continuously so that it doesn't stick to the bench.
Fold the icing in half and put the folded half onto the middle of the cake and then unfold to cover the entire cake. (The icing can be gathered together and re-rolled if you have trouble with splitting or tearing, before you put it onto the cake. Once it touches the buttercream though it is on the cake and can't be moved.)
Smooth down the side pushing out the folds. You should be able to get rid of all of them except the one. Cut a v into the icing and remove the excess, then push it together and smooth over with a piece of plastic or shiny satiny material. Cut the icing off at the bottom of the cake around the plate. (Plan to put decorations onto rough sections).
I rolled out a long black ribbon and cut it into a 3 in or 7 cm size. I wrapped this around the base of the cake and formed the end into a black rose. This is optional for you.
To make edible glue for sticking on the decorations, put the egg white into a bowl ( don't use a whole white!) and start mixing in the sifted icing sugar until you have a paste that is easy to spread. This paste will look better if it is coloured black so add a drop or two of colour and re- adjust the thickness by adding some more icing sugar.
Use this paste on the end of a toothpick to paste on whichever decorations you would like to use. Use a small brush or a pastry brush to get rid of any icing sugar stuck to the black icing.
To make the bloody syrup, mix red food colouring with glucose syrup ( available in the supermarket)