Prepare the Cake Layers: Preheat the oven to 340°F (170°C). Lightly butter the bottom of a 9-inch (24 cm) springform pan and line it with parchment paper.​

In a clean bowl, beat 2 egg whites until stiff peaks form. Gradually add 2 tablespoons of sugar, continuing to beat until the sugar dissolves.​

Gently fold in ½ tablespoon of flour and ½ cup (50g) of ground hazelnuts until well combined.​

Spread the batter evenly in the prepared pan and bake for 20-25 minutes, or until golden brown.​

Repeat this process two more times to create a total of three cake layers. Allow them to cool completely on wire racks.​

Prepare the Buttercream Filling: In a saucepan, whisk together the egg yolks and cornstarch. Gradually add the sugar and milk, whisking continuously to prevent lumps.

Place the saucepan over low heat and cook the mixture, stirring frequently, until it thickens into a pudding-like consistency (about 6 minutes).​

Remove from heat, stir in the vanilla extract, and cover with plastic wrap directly on the surface to prevent a skin from forming. Let it cool completely.​

Once cooled, beat the softened butter until fluffy. Gradually add the cooled pudding mixture, one tablespoon at a time, beating well after each addition until smooth.​

Prepare the Caramel Filling: In a non-stick pan over low heat, melt the sugar until it turns a deep amber color, being careful not to let it burn.​

Pour the caramel onto a parchment-lined baking sheet and let it cool until hardened.​

Break the hardened caramel into pieces and process in a food processor until finely ground.​

Whip the heavy cream until stiff peaks form. Gently fold in the ground caramel and ground hazelnuts until well combined.​

Assemble the Cake: Place the first cake layer on a serving platter. Spread one-third of the buttercream filling evenly over the layer.

Top with one-third of the caramel filling, spreading it evenly.​

Repeat this process with the remaining cake layers and fillings.​

Use the reserved buttercream to frost the sides of the cake.​

Garnish: Sprinkle the top and sides of the cake with ground hazelnuts.​

Lightly dust the top with unsweetened cocoa powder for a decorative finish.​

Chill and Serve: Refrigerate the assembled cake overnight to allow the flavors to meld and the cake to set properly.​

Before serving, let the cake sit at room temperature for about 15 minutes for optimal flavor and texture.​