Preheat the oven to 338°F (170 °C). In a water bath, melt the butter, sugar and chocolate on low heat. Leave it to cool for 10 minutes.
Stir everything until you get a smooth mixture, put it into a pre-greased and lightly floured baking tray. Put it to bake for about 1 hour, being careful not to burn it and checking whether it is ready.
Meanwhile, make the ganache, by melting 9 oz (250 g) chocolate with the cream and 1 teaspoon instant coffee in a water bath. Leave it to cool slightly.
Set aside 1/3 of the mixture to spread it on the top of the cake. Fill the remaining mixture into an icing piping syringe with a thin nozzle. Insert the nozzle into random spots on the cake and squeeze.
That is how you will obtain the chocolate parts in the cake. Finally, brush the top with the set aside portion of ganache and make decorations as desired.