Preheat the oven to 350 degrees F. Grease the bottom and side of an 8 - 9.5" springform pan with butter. Use the springform pan to trace and cut a circle of wax paper then place the wax paper circle on the bottom of the greased pan. Set aside.
In a the bowl of a stand mixer with whisk attachment or in a large bowl with hand held beater, beat the eggs whites until stiff. Set aside. In a separate bowl, beat the egg yolks with the sugar until foamy. Add the breadcrumbs, spelt flour, baking powder, and ground hazelnuts. Beat on low until combined. Add the egg whites and fold gently until just combined.
Pour mixture into the springform pan and spread mixture evenly. Bake for 45 minutes. Remove the cake from the oven, let cool and then cut cake into 3 layers. The top layer may have collapsed a little but that's ok as this will be hidden by the filling.
In a small bowl pour the gelatine over 1/4 cup of cool water. Add 1/4 cup boiling water and stir constantly until completely dissolved. Set aside. In another small bowl, mix the cocoa powder, instant coffee and sugar with 1-2 tbsp of water to help it combine. Set aside.
In a the bowl of a stand mixer with whisk attachment or in a large bowl with hand held beater, beat the whipping cream with the gelatine until stiff. Add the instant coffee mixture and beat until combined. Transfer approximately 1/2 cup of the filling to a pastry bag with a flower tip.
Place the bottom layer of cake on a cake plate or stand. Spread a thin, even layer or marmalade or jam on top and 1/3 of the remaining filling. Place the second layer on top, sprinkle with rum (optional) and spread another 1/3 of the remaining filling evenly on top. Top with the last layer of cake.
Fill the cracks on the sides of the cake with cream, then frost the sides and top of the cake with the rest of the cream.
Shave the chocolate with a large knife or potato peeler. Sprinkle chocolate around the base of the cake then lift and gently press the shavings onto the sides of the cake with a spatula. Pipe 8 - 12 florets on the top of the cake around the edges and top each floret with a hazelnut or coffee bean (in this recipe I have used chocolate covered coffee beans).
Chill and refrigerate for a minimum of 8 hours up to 24 hours before serving to let all the flavors mingle.