For me, chocolate and oranges are a timeless dessert combination. If we add caramelized hazelnuts and peanuts to that combination, we get a match made in cake heaven. Cake layers are soft and tender, the filling is smooth, creamy, and deliciously crunchy because of the said caramelized nuts, with just a little burst of flavour from the candied oranges; and the frosting is like a thick, rich fudge. To be honest, each element could be eaten separately, they are all that good. As far as the hazelnuts and peanuts combination, I leave that up to you to choose how much you want from each. And if you do not have tiny cake pans or simply do not want to use them, you can bake the cake in a standard cake pan (23 cm, 9"), just bake it for a little longer, say 25 minutes.
For the cake
8 tablespoons plain flour
6 tablespoons unsweetened cocoa powder
2 teaspoons baking powder
8 tablespoons sugar
6 tablespoons milk
6 tablespoons vegetable oil
1 teaspoon vanilla bean paste
For the filling
120 grams butter, softened
200 grams icing sugar, sifted
2-4 tablespoons heavy cream
100 grams candied orange slices, minced
100 grams caramelized hazelnuts and peanuts
For the fudge frosting
100 grams dark chocolate
7 tablespoons heavy cream
2 tablespoons butter
To make the cake, sift together the flour with the cocoa powder and baking powder, and set it aside. Take a large bowl, add the eggs, and sugar, and whisk vigorously for about a minute, to blend it well and make the batter a bit thicker. Add in the milk, oil, and vanilla bean paste, and blend really well. Sift in the dry ingredients and briefly whisk it, just until incorporated. Take three small round cake pans (10 cm, 4"), grease and flour them well, and pour in equal amounts of batter in each pan. Bake them in a preheated oven, at 180˚C (350˚F), for about 15-20 minutes. Check them with a toothpick to make sure they aren't overbaked. Remove them from the oven and let them cool for about 10 minutes in the pans, then take them out and let them cool completely on a wire rack.
For the frosting, sift the icing sugar twice, and set it aside. Mince the candied orange slices and finely crush (or grind) the caramelized hazelnuts and peanuts. Place the softened butter in a large bowl and beat it with an electric mixer on high for about 2 minutes, to make it light and creamy, then add the icing sugar in a few additions, blending really well after each. Finally, add the heavy cream gradually, still whisking on high, until you achieve your desired thickness of frosting. Once you are happy with the frosting, fold in the minced oranges and crushed hazelnuts and peanuts.
The cakes should be cool by now, so level them as much as possible and proceed to assemble the cake. Place the first cake layer on a small serving plate, then pipe (or spread) on half of the filling. Place another cake layer on top of that, and pipe on the rest of the filling. Finally, place the last cake layer on top, gently press with the palm of your hand, and place the entire cake in the fridge for at least 4 hours.
To make the fudge frosting, chop up the chocolate, dice the butter, and place them in a heavy-bottomed saucepan, then pour over the heavy cream, and melt everything over medium heat. Once everything is well blended, remove from the heat and let it stand at room temperature until thickened and slightly matte. Take the cake out of the fridge, decorate it as desired and serve immediately. Yields 6 small slices.