For the cake use a fi20cm (8 inch) round baking tin and spray the bottom with baking spray or butter & lightly flour it.
In a bowl, add flour, baking powder and 2 tbs cacao powder and combine well.
Separate egg whites and yolks. In a large bowl, add 75 g sugar to egg whites and whisk through until fluffy (use an electric mixer).
In a separate bowl combine egg yolks and the remaining 75 g sugar, add hot (not boiling!) water and whisk until the yolks increase in size. Add the flour mix to the egg yolks slowly (by spoon) and continue mixing it in with a spatula, until you use all of the flour mix. Then, add oil to the egg yolks and combine well. Lastly, add the mixture to the egg whites and fold it in gently until thoroughly combined.
Pour the cake mixture into the baking tin and put into the preheated oven. Bake for about 50-60 minutes. You can check if your cake is done by inserting a toothpick into the cake. If it comes out clean, your cake is ready to be removed from the oven. Set aside to cool, then slice the sponge cake two times horizontally to achieve 3 cake layers.
Mix dark rum (or bourbon) with milk. Gently soak the 3 sponge layers with the milk mixture. You can also reduce with water for a moister soak. Note: I did not add any sugar as I don't like it too sweet, but if you want, you can add some sugar to water and bring to a boil to melt the sugar.
For the chocolate frosting: In a bowl whip the cream until firm, then add the mascarpone and Nutella. Fold in with a spatula and combine well.
Assemble the cake. Put the first spongecake layer on your serving plate. Put chocolate frosting in a plastic bag, twist the top of the bag and cut a hole in the bottom. Squeeze the frosting onto the first spongecake layer in a circular move from the outside to the center of the cake. Add the second sponge layer and repeat. Add the top layer and repeat. Use a spatula or knife to distribute the frosting evenly on top of the cake and on sides. Dust the top layer with cacao powder and decorate with some pine and cinnamon sticks. Refrigerate for at least 2 hours, or overnight. Serve chilled.