Mix flour, cacao, sugar and water and simmer for four minutes. When simmering, approximately at grade 4, stir constantly to prevent the mixture from getting burnt. Remove from hob and mix in chocolate. Leave to cool completely, you can even wait till the following day. Then mix in softened shortened fat. Make sure the mixture is well beaten without any solid pieces of fat.
Before piping the peaks, put the compound into the fridge, but do not leave it to turn fully solid, so that you can pipe it with a piping bag. In the meantime ice the sponge biscuits with chocolate. This will prevent the sponge biscuits from softening. Pipe the compound with the special piping nozzle onto the sponge biscuits and put into the fridge. You can bake your own sponge buflers. (The piping nozzle has a little hole on the side and this must always stay out). The rule for using the piping nozzles is that they have to be very cold, the best way is to freeze them for a bit. Do not forget to leave some compound to cover the peaks. Thicken the eggnog with powdered milk, fill the peaks with the egg nog and close the peak by piping through a decorative piping nozzle. Put back in the fridge. Melt the chocolate with shortened fat and dip the chilled peaks in it.