Drain cherries from their juice, place them in a dish and pour rum over the cherries. Let them soak in rum for at least 12 hours.
Beat 8 eggs (no need to separate them) with sugar until it’s three times in volume. Combine flour together with cacao. Using a spatula, fold in flour by thirds; be very gentle with the dough so you don't over mix it and lose the fluffiness. Place butter in a greased 9 inch pan. Bake it for 40 minutes at 350F, check it with a wooden toothpick. If the cake is ready, dough should not stick to the toothpick.
Cut off top thin layer off the sponge cake and set it aside, this so in the end you can have flat nice top to over your cake with once it’s filled.
Cut line close to edges on the inside. Rip out the inside of the cake where it ends up looking like bowl. Rip cake in small pieces, set aside.
Whip together 1 cup sugar and whipping cream. Make sure bowl and whipping cream is very cold, it will make cream firm.
Drain all rum from cherries. Mix together pieces from sponge cake, cherries and about 90% of the cream.
Fill the cake bowl with the mixture, apply a little bit of cream. Cover with the cake lid. With remaining cream cover the cake. Refrigerate it while you prepare chocolate ganache.
Bring whipping cream to a boil, pore it over chocolate chips, stir until smooth. Let ganache cool a little.
Place chocolate ganache in a ziplock or a piping bag. Drizzle chocolate on the edges of the cake, letting the chocolate drip off the sides. Apply the remaining chocolate ganache to the top of the cake. Use remaining cherries to decorate the outside of the cake.
Keep cake refrigerated overnight.