Fill a mason jar with 3 cups of drained sour cherries. Add 1/2 cup of sugar and 1/2 cup rum and close the duo tightly. Shake vigorously until all the ingredients are well mixed. Let it sit in the fridge for 2-3 days making sure to shake the jar occasionally until the sugar dissolves.
Sift 3/4 cup cocoa powder and 2 cups of flour together. Then set aside.
In a large heatproof bowl, beat 10 eggs on high speed with a handheld mixer. Mix until the eggs become foamy, then add in 2 1/2 cups sugar. Keep mixing for another 5 minutes.
Transfer the bowl of beaten eggs and sugar on top of a pot with about 1 inch of simmering water (double boiler).
Keep the pot over low heat and constantly mix the mixture with an electric mixer. About 10-15 minutes. It should double in volume.
Gently fold in the cocoa and flour mixture using a whisk.
Pour the cake batter into a greased 12 inch round baking pan. Bake at 350 degrees Fahrenheit for 20 minutes and 320 degrees Fahrenheit for 40-50 minutes. Flip the cake onto a cooling rack and let it cool completely. I usually let it cool overnight.
Using a serrated knife, slice off the top of the cake. Then run a knife along the edge of the cake leaving about 1/4 inch of the rim. You can leave less, that's even better, but there's always a risk of having it fall apart if it's too thin.
Once the cake is cut around the edge, remove all of the insides, crumble it up and set aside. Leave about 1/4 inch at the bottom as well. You should end up with a hollow cake or a "cake shell".
For the cream:
In a saucepan lightly beat 4 eggs with 1/2 cup of sugar. Then whisk in 1/2 cup cocoa powder. And add 1/2 cup milk.
Place the saucepan over low heat and stir constantly until the mixture thickens. Do NOT let the egg mixture boil or else you will end up with chocolate scrambled eggs.
While the chocolate mixture is cooling down, beat 4 sticks of softened butter with 1 1/2 cups sugar. Beat until the butter becomes light in color and fluffy.
Strain all the liquid out of the rum soaked cherries and slowly pour the rum liquid into the whipped butter while the mixture is on medium speed. Make sure to pour very slowly to prevent the butter from separating.
Add the cooled chocolate mixture to the whipped butter and mix just to combine.
Take all of the cake crumbs and blend it into the chocolatey butter using the paddle attachment on medium high speed. Then add in the strained cherries and mix just to combine.
Fill the cake shell with the chocolate butter and crumbled cake mixture. Be very gentle when filling the cake. Support the sides of the cake as you press the filling in. Smooth it out with a flat decorating spatula to give it a clean finished look.
At this point you can leave it as is or coat it with a chocolate ganache. For the ganache on this cake is used 16 oz milk chocolate, 8 tbsp butter, 8 tbsp honey, and 1 1/2 cups heavy cream.