Chocolate Sponge Cake

Preparation

1. Remove the butter from the refrigerator approximately one hour before use, to bring it to room temperature.
2. Crush the hazelnuts with a hand blender or food processor until you achieve a fine and homogeneous texture.
3. Preheat the oven to 170ºC for half an hour before starting to bake to ensure it maintains the correct temperature.
4. 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.
5. Separate the egg yolks from the egg whites and set them aside in different containers.
6. 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.
7. 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).
8. Melt the chocolate in a double boiler, ensuring that no water gets in, as this can ruin the chocolate and make it unusable.
9. Gently warm the butter to a soft consistency until it is fully melted, approximately at 30ºC.
10. Gradually incorporate the melted chocolate into the bowl with the yolks, stirring gently with a spatula from the bottom upwards, until well combined.
11. Add the melted and lukewarm butter, stirring gently and always from bottom to top to maintain the light texture.
12. Incorporate one-third of the whipped egg whites into the chocolate batter, stirring gently to avoid losing volume.
13. 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.
14. Line the mold again with baking paper at the base, greased with butter, to prevent sticking.
15. 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.
16. Bake at 170ºC for about 35 to 40 minutes, until a toothpick inserted in the center comes out clean.