Steps

• To prepare the cocoa sponge cake, start by gathering the eggs with the contents of the vanilla pod and the sugar in a bowl.
  Mix with electric whisks or in a stand mixer for about 16/20 minutes at medium speed until you get a light, very fluffy, and frothy mixture that, when lifted, should form a sort of ribbon and remain visible for a few seconds before sinking.

  

• Meanwhile, sift the flour together with the starch, baking powder, and cocoa powder.
  Mix the powders well.

  

• Incorporate the powders by sprinkling them in and gently mixing with a spatula from bottom to top, to avoid deflating.
  Mix until a homogeneous mixture is obtained.
  Pour the mixture into a 26 cm diameter mold, greased and floured, and level gently with a scraper, without beating or pressing.
  Bake in a preheated oven, in static mode, at 329-338°F (165-170°C) for about 30-35 minutes, or until a skewer inserted in the center of the cake comes out dry.
  Do the skewer test to see if it’s cooked before removing it from the oven.

  Once cooked, turn the sponge cake upside down and let it cool.

  

• Melt the chopped chocolate together with the cream in a bain-marie, stirring occasionally with a spatula. Once the mixture is homogeneous, remove it from the heat and stir again with a whisk to cool it down, add the spoonful of Nutella and let it cool completely.

  We will need it cold from the fridge.

  (To be whipped at a later time).

  

• Meanwhile, also prepare the syrup. Heat the water in a saucepan with the sugar, stir and bring to a boil, then turn off, add the rum, stir, and let it cool.

• Meanwhile, spread the Nutella on a sheet of parchment paper trying to create two “disks” the same size as the cocoa base, place it in the freezer and let it freeze completely.

  
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• Once the sponge cake is completely cooled, if necessary, cut the surface to make it perfectly flat, then cut it to obtain three discs of the same thickness, it’s useful in this step to use a long serrated knife.

  Place a disc of sponge cake, which will be the base, on a plate or a cake board then soak it with about one third of the prepared syrup, spread it with part of the whipped cream.

  (I used a piping bag to help myself).

  

• Now gently take a Nutella disk (which will be cold and will detach very easily) and place it on top of the cream.

  Repeat with the sponge cake disc followed by the cream and Nutella disk.

  (You can use a spatula or piping bag, then place the second sponge cake disc on top, soak it again with about a third of the prepared syrup, and add more cream, saving a little to use as a decoration for the cake).

  Now place the last sponge cake disc and soak it with the remaining syrup.

  Apply a light layer of cream and put the cake in the fridge while we whip the chocolate ganache.

  

• Once the chocolate ganache has cooled (about 30 minutes – 1 hour), place the cream in a bowl and whip it with electric whisks: it will take 2-3 minutes.

  Retrieve the cake and with a spatula cover the surface and sides with part of the whipped cream, for this step it is very convenient to use a rotating cake stand, then transfer the remaining whipped cream into a piping bag with a star tip and decorate the cake as you like, also use the remaining chocolate ganache for decoration.

  Finally, finish the decoration with chocolate sprinkles.

  I can say for the decoration, feel free to do it as you like.

  

• Place the cake in the fridge to firm up for 1 hour and then serve.

  Enjoy your meal