Preheat the oven to 170°C (340°F). Line the bottom of a 24cm (9-inch) springform pan with parchment paper.

Prepare three separate cake layers: For each layer, whisk 2 egg whites until stiff peaks form, gradually adding 2 tablespoons of sugar. Gently fold in 0.5 tablespoons of flour and 50g of ground hazelnuts.

Spread the batter for one layer into the pan and bake for 20 minutes. Repeat the process to create three identical layers in total. Allow all disks to cool completely.

Prepare the yellow filling: In a heavy-bottomed saucepan, whisk 6 egg yolks with 6 tablespoons of sugar and 3 tablespoons of cornstarch. Gradually pour in the milk while whisking to avoid lumps.

Cook the mixture over medium-low heat, stirring constantly until it reaches a thick custard consistency. Remove from heat, stir in vanilla extract, and cover the surface with plastic wrap to cool completely.

In a separate bowl, cream the softened butter until fluffy, then gradually incorporate the cooled custard one tablespoon at a time until smooth.

Prepare the crunchy filling: Place 200g of sugar in a non-stick pan over low heat to create a dry caramel. Once amber-colored, pour onto oiled parchment paper, let cool, and then crush into a fine grit with a rolling pin.

Whip the heavy cream until stiff peaks form. Fold in the crushed caramel and the remaining 130g of ground hazelnuts.

Assemble the cake: Place the first hazelnut disk on a platter, spread one-third of the yellow filling, followed by one-third of the crunchy filling. Repeat for the next two layers.

Cover the top and sides with the remaining filling or additional whipped cream. Refrigerate for at least 6 hours (preferably overnight) before serving to allow the layers to set.