1. Bring 100g sugar and 100ml water to the boil and leave on a rolling boil for around 2 minutes to form a sugar syrup. Leave to cool.
2. Cut the milk chocolate couverture into small pieces. Heat up the milk and crumble in 50g marzipan and the couverture pieces. Stir until the ingredients have melted and then stir in the rum to form a smooth mixture.
3. Using a hand mixer, blend together the soft butter, 100g sugar and vanilla seeds until very creamy. Add the egg yolks one after the other, mixing them in well each time. Next, stir in the marzipan couverture milk mixture. Beat the egg whites with a pinch of salt until stiff, gradually adding 100g sugar as you do so.
4. Fold the beaten egg whites evenly into the egg yolk mixture. Sieve in the flour, cornflour and cocoa powder and fold together with a dough scraper.
5. Purée 200g marzipan together with the orange juice, zest and the sugar syrup. Line the base of a (24cm) springform cake tin with baking paper; clamping the paper into the ring when you do this.
6. Spread a thin layer of mixture across the bottom of the tray and bake under a hot grill for between 30 seconds and 1 minute, until brown. Do not leave the oven grill unattended.
7. Spread another layer of mixture across and bake in the same way. Next, spread a layer of the marzipan mixture across the top using a brush and bake in the same way as with the previous layers. Continue in this way, adding one marzipan layer after every two layers of cake mixture. At the end you will have 12 cake layers and 5 marzipan layers. Cover the finished cake, switch off the oven and leave the cake to rest in the oven for approx. 10 minutes. Wrap in foil and leave to cool overnight.
8. Warm up the cake icing as per the packet instructions, spread evenly over the cake and allow to set for around 30 minutes. Add patterns if you wish and dust with icing sugar.