Grate marzipan. Cream fat, salt, sugar and vanilla sugar with the whisk of the hand mixer. Stir in the eggs one after the other. Mix flour and baking powder. Stir in together with the milk.
Dissolve espresso powder in 2 tablespoons of hot water. Halve the dough, stir into one half of marzipan and stir in cocoa and espresso into the other half. Pour light-coloured dough into a greased, flour-dusted box form (30 cm long, 1.75 litres capacity). Spread the dark dough over it. Marble with a fork. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 1 hour. Leave to rest in the pan for about 10 minutes. Turn out onto a cake rack and let it cool down. Halve the cake twice lengthwise.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 1 hour. Leave to rest in the pan for about 10 minutes. Turn out onto a cake rack and let it cool down. Halve the cake twice lengthwise. Stir the jam until smooth and fill the cake with it. Dust the cake with icing sugar and cut into slices
1 1/4 hours waiting time