In a saucepan, combine cornstarch, cocoa powder, and sugar. Add in cold milk, whisk until combined.

On medium heat, bring mixture to a boil stirring constantly. Lower the heat and continue stirring until the mixture gets thick like a pudding. Set aside, cover the surface of the pudding with plastic wrap and allow it to cool down.

Meanwhile, beat butter with powder sugar until creamy.

When the pudding is cool, incorporate butter spoon by spoon, into the mixture, using a hand mixer. Add rum extract and ground walnuts. Set aside.

Preheat oven to 350F/180C.

Separate the eggs.

Mix the flour with the baking powder. Set aside.

Beat the egg whites to a soft peak consistency with a pinch of salt, then add the sugar and continue mixing until sugar is dissolved and egg whites get to a stiff pick.

Incorporate orange zest and egg yolks one by one, folding slowly, to make sure you do not lose the air in the egg whites.

Finally, add the flour with the baking powder and fold again to obtain a smooth batter.

Place parchment paper on the bottom.

Pour the batter into the cake pan and bake at 350F/180C for 25-30 minutes.

Test in the middle with a toothpick to make sure it is done. The toothpick should come out clean.

Remove the cake from the pan and allow it to cool on a metal rack.

Cut horizontally in 2 even layers.

Mix sugar and water in a medium pot and bring them to a boil. Let them simmer for 1 minute, then remove and allow it to cool.

When cool, add the vanilla extract.

Place a layer of the cake on the bottom of the same springform cake pan.

Using a brush, brush the cake layer with the sugar syrup.

Pour the entire cream filling on the cake layer and spread it evenly.

On a different plate, place the second layer of the cake and brush it with syrup.

Place the second layer of cake on top of the cream filling and press gently on each side.

In a medium bowl, break both milk and dark chocolate in smaller pieces.

In a small pot, bring the heavy cream to a boil and remove immediately.

Pour the hot heavy cream over the chocolate. Using a spatula, mix gently until the combination becomes silky and creamy.

Pour the chocolate over the cake. (remember that your cake is in a springform, so the warm chocolate cream will stay on top of the cake)

Place the cake in the fridge to cool down completely for 1-2 hours.

Take the cake out of the fridge and remove the springform ring from around the cake.

Place the cake on a cake stand or a platter.

Whip the heavy cream together with the instant coffee powder.

Cover with whipped cream ONLY the sides of your cake with a flat spatula. Apply a thick coat around the cake so there is room to press in the nuts without them poking into the cake.

Lift the plate up over a shallow bowl or baking sheet that’s wider than the plate. With your free hand, scoop up a large handful of ground walnuts. Using just a few at a time means you’re more likely to smudge the frosting, so pick up more than you need and reuse any that fall.

Gently press your handful of nuts against the side of the cake. Some nuts will likely fall into the bowl or on the baking sheet below; simply collect them to use again. Rotate the cake as you work so you end up with an even coating of nuts all the way around.

When you finish decorating, chill the cake for at least 20 minutes before cutting into it.

If you have leftover whipped cream, decorate the face of the cake with little whipped cream rosettes.