Cream Room Temperature butter until light and fluffy (apx 2-3 minutes) Then add in the sugar, vanilla sugar and rum. Cream for another 3-4 minutes. Now gradually add in the eggs while still whisking. Last fold in the flour and ground almonds until well combined. Preheat the oven at 190C or 375F with convection.
Line a 9 Inch springform with parchment paper and grease it well. Spred 2-3 tablespoons of batter evenly on the bottom of the form. Bake for 6-7 minutes until golden brown. Allow to cool for a couple of minutes and then spread another thin layer on top of the baked layer. Bake and repeat until you have five to six layers. Take out of the springform and set on a cooling rack. Clean the form and repeat with the remaining batter. You need a total of 5 - 6 layers for each of the two cake sides (top and bottom)
Knead the marzipan with the rum and confectioners sugar until malleable. Dust your working surface with powder sugar and roll into a 9 inch circle. Use the bottom of the springform to trim edges. You can roll the trimmings in to the center or eat them :D Place the marzipan layer over the bottom half and set the top half over it. Its best to place the top layer downside up so you have a perfectly flat top.
Ganache and Pistachios
Melt the chocolate over a how water bath in a heat proof bowl. Once it has fully melted, take it off the steam and whisk in the heavy cream. Cool for a few seconds (but don't let it set) and then pour over the cake. Using a confectionary knife or the back of a spoon, level the top and drip the excess ganache evenly over the edges. You can fix the edges with a bit of chocolate. Dont stress if it's not even, the pistachios will hide any imperfections. Sprinkle the chopped pistachios over the ganache and allow to cool. Serve with some fresh cream, tea or coffee.
ProTip: You can layer apricot jam between the cakes for extra flavour.