Bring the egg whites and unsalted butter to room temperature.

Preheat the oven to 180°C and line the 24 cm round cake pan with parchment paper.

Whip 3 egg whites until foamy, then gradually beat in 60 g granulated sugar until stiff peaks form.

Fold 85 g ground hazelnuts and 1 tbsp breadcrumbs into the meringue until just combined.

Spread the batter in the prepared pan and bake for about 10 minutes.

Cool the cake layer completely, then repeat the layer-making process three more times for 4 layers total.

Place the heatproof bowl over barely simmering water without letting the bowl touch the water.

Whisk the 12 egg yolks with 100 g granulated sugar over steam until thickened.

Remove the yolk cream from the heat and stir in 150 g dark chocolate until melted.

Mix 250 g hazelnut spread into the warm chocolate cream until smooth.

Beat 250 g room-temperature unsalted butter into the warm cream until fully incorporated.

Cover the cream directly with plastic wrap and chill it until completely cool.

Whip 200 ml whipping cream for filling to firm peaks, then fold it into the cooled hazelnut cream.

Place the first cake layer on the cake plate and spread over one-third of the filling.

Repeat the layering with the next two cake layers and the remaining filling.

Place the fourth cake layer on top without filling and chill the assembled cake until firm.

Heat 200 ml whipping cream for ganache until it reaches a boil, then pour it over 200 g baking chocolate.

Stir the ganache until smooth, then refrigerate it for 15–20 minutes until spreadable.

Spread the chilled ganache evenly over the firm cake before serving.