Hazelnut and Chocolate Filled Cake

Method

1. In a large bowl, whip sugar, whole eggs, egg yolk, and a pinch of salt with electric beaters or a planetary mixer for 8-10 minutes until the mixture is light, fluffy, and pale.
2. Meanwhile, sift together the 00 flour, unsweetened cocoa powder, and potato starch (fecola). Sift twice for a lighter sponge.
3. Gently fold the dry ingredients into the egg mixture in two or three additions, using a spatula and lifting from the bottom.
4. Grease a cake pan or line with parchment paper, then pour in the batter.
5. Bake in a static oven at 180°C (350°F) for about 30-35 minutes.
6. Prepare the soaking syrup: in a saucepan, combine water and sugar. Bring to a boil while stirring, then remove from heat and let cool. Add rum and mix.
7. Prepare the cream: in a bowl, combine mascarpone, hazelnut spread, and powdered sugar. Mix with a spatula until smooth.
8. In a small saucepan, heat milk with gelatin sheets (previously hydrated in cold water) until the gelatin dissolves. Let it cool to lukewarm.
9. Pour the milk mixture into the mascarpone mixture and mix immediately.
10. Fold in the whipped cream gently from bottom to top.
11. Refrigerate the cream for a short time so the gelatin begins to set.
12. For assembly: use a serrated knife to remove the crust from the top of the sponge cake. Cut the cake horizontally into two layers.
13. Place the original bottom layer on a wire rack (this will become the top). Soak it with the syrup.
14. Pipe about half of the cream onto the layer and spread evenly with a spatula.
15. Soak the second disk (the cut top that will become the bottom) on the inside, then invert it onto the cream, leaving the soaked side facing down. Also soak the top surface.
16. Refrigerate the cake while preparing the glaze.
17. Prepare the glaze: in a saucepan, heat cream to boiling. Remove from heat, add chopped chocolate, and stir with a whisk until melted and smooth. Let it cool to about 50°C (120°F).
18. Pour the glaze over the cake on the rack. Tap the rack to distribute evenly.
19. While the glaze is still soft, press hazelnut pieces onto the sides of the cake.
20. Transfer the cake to a serving plate using two spatulas. Refrigerate until the glaze sets.
21. Decorate the surface with the remaining cream using a piping bag fitted with a star tip.
22. Keep the cake refrigerated until serving.