Mix the contents of the sachet with the milk, softened butter and peanut oil until smooth. Do not over-whisk. Oil the cake tins, pour in the mixture and bake in a preheated oven at 160°C for around 25 minutes, depending on size.
Melt the chocolate, spread, sprinkle with Aztec gold and decorate as desired.
Serve the cake with the chocolate wafer and the zabaione filling.