Preparation

• Remove the butter from the refrigerator approximately one hour before use, to bring it to room temperature.
• Crush the hazelnuts with a hand blender or food processor until you achieve a fine and homogeneous texture.
• Preheat the oven to 170ºC for half an hour before starting to bake to ensure it maintains the correct temperature.
• Line the base of the springform pan with baking paper and grease the base with butter. It is not necessary to grease the sides of the pan.
• Separate the egg yolks from the egg whites and set them aside in different containers.
• Beat the egg whites with 115 grams of sugar using an electric whisk until firm peaks form, a process that may take between 8 to 10 minutes.
• In another large bowl, beat the egg yolks with 35 grams of sugar, the crushed hazelnuts, and the vanilla using an electric whisk until they achieve a whitish tone and at least double in volume (approximately 10 to 15 minutes).
• Melt the chocolate in a double boiler, ensuring that no water gets in, as this can ruin the chocolate and make it unusable.
• Gently warm the butter to a soft consistency until it is fully melted, approximately at 30ºC.
• Gradually incorporate the melted chocolate into the bowl with the yolks, stirring gently with a spatula from the bottom upwards, until well combined.
• Add the melted and lukewarm butter, stirring gently and always from bottom to top to maintain the light texture.
• Incorporate one-third of the whipped egg whites into the chocolate batter, stirring gently to avoid losing volume.
• Add the rest of the whipped egg whites and, before stirring again, sift the flour and the crumbs of sponge cake or ladyfingers over the mixture. Stir with a manual spatula, from bottom to top, until homogeneous.
• Line the mold again with baking paper at the base, greased with butter, to prevent sticking.
• Fill the mold with the batter and smooth the surface with a long spatula or the non-cutting edge of a long knife to ensure even baking.
• Bake at 170ºC for about 35 to 40 minutes, until a toothpick inserted in the center comes out clean.