For the cake layers
- Preheat the oven to 160ο C (320ο F) set to fan.
- In a mixer’s bowl add the butter, the sugar, and beat with the whisk attachment at high speed, for 4-5 minutes, until the mixture is fluffy.
- Add 2-3 tablespoons of the flour and put the eggs in, one by one. Wait for each one to be incorporated before adding the next.
- Add the yogurt, the vanilla extract, the orange zest, and beat until the ingredients are homogenized.
- In a bowl mix the flour, the baking powder, and the salt.
- Remove the bowl from the mixer and add the flour. Mix softly with a serving spoon.
- Butter and flour 3 cake pans, 20 cm each, and divide the mixture into them. Spread the mixture with your hands. If the mixture sticks to your hands, wet them with a little water.
- Bake for 30 minutes. Remove and let them cool.
For the caramelized hazelnuts
- Place a frying pan over medium heat.
- Add the sugar, the water, salt, and allow 3-4 minutes for the sugar to melt and become a caramel.
- Heat the hazelnuts in the microwave for ½ minute, at 800 Watt. Remove and add them to the frying pan with the caramel. Mix for 1-2 minutes until they are well caramelized.
- Remove and add them to a baking pan lined with parchment paper, and let them cool well.
- Transfer into a blender and grind them until they break down. Do not grind them to fine crumbs. Set aside.
For the buttercream
- Place a glass bowl over a pot with boiling water in order to create a bain-marie.
- In the bowl add the egg whites, the icing sugar, the salt, and mix with a whisk for 3-4 minutes until the mixture is fluffy.
- Transfer into the mixer’s bowl and beat with the whisk attachment at high speed, for 2-3 minutes, until the mixture thickens.
- Gradually add the chocolate, the butter cut into cubes, and beat very well for 4-5 minutes so that the mixture thickens and cools.
- On your serving platter, place 3 strips of parchment paper shaped like a triangle.
- Cut the cake layers horizontally in half, and set them aside.
- Place one half of the cake at the base of the platter. Cover its surface with 1-2 spoonfuls of the buttercream, the 1/6 of the hazelnuts and cover with the second half of the cake. Follow the same process for all of the cake layers and the buttercream. Lastly, use a spatula to cover the sides of your cake with the buttercream.
- Decorate with the caramelized hazelnuts and serve.