Prepare the cake layers from 5.5 oz (150 g) dark chocolate melted in a water bath. Beat the butter with 2/5 cup (100 g) of sugar, add the egg yolks one at a time, then the cooled chocolate, flour and beaten whites with a pinch of salt.
Pour the mixture into a greased round form that's 10" (24 cm) in diameter and bake for about 40 minutes in a preheated oven at 356°F (180 °C). The center may be slightly creamy. Remove from the form and cool.
Heat the cream for the filling, add 7 oz (200 g) dark chocolate, and once it melts, remove it from the fire, let it cool and put in the refrigerator for at least 2 hours. Then beat it into a fluffy cream with a mixer, while also adding the rum.
Cut the layers in half and fill them with 2/3 of the cream. Use the rest of the cream for decoration. Spread the cake with a thin layer of cream on the top and sides. To prepare the cake decoration, use different colored chocolates.
Melt them in a water bath and use a pastry bag or other utensil to apply.