Sponge:

• Preheat the oven to 180°C (350°F). Line a 25/35 cm (10x14 inches) baking tray with parchment paper.
• In a bowl, combine the flour with the ground walnuts, vanilla sugar, and baking powder.
• Mix the butter with the sugar until it becomes creamy (5-10 minutes). Add alternately a whole egg and a tablespoon of flour. Mix well and repeat until you have added the 4 whole eggs. Add the remaining dry ingredients.
• Whisk the egg whites with a pinch of salt. Gently fold the egg whites into the egg and buttercream with upward movements. Pour the mixture into the baking tray and smooth it out.
• Bake for 30-35 minutes. After passing the toothpick test, transfer to a cooling rack.
• When completely cooled, cut the cake vertically into two smaller pieces of 25/17 cm (10x6.5 inches). Cut each piece horizontally into 2 thinner pieces. This will give four 25/17cm (10x6.5 inches) sized pieces.

Caramel cream:

• Add the sugar together with the water in a small thick-bottomed saucepan. Allow the sugar to melt and boil until it turns a deep copper color. Turn off the heat and add the butter. Stir vigorously to homogenize the mixture. Add the milk and mix well. Leave the mixture on low heat.
• Whisk the egg yolks gently. Slowly pour the caramel cream over the yolks. Return the mixture to the stove and leave it over a low heat. Stir continuously until the cream begins to thicken. It will take about 8-10 minutes (on low heat). Turn off the heat.
• Hydrate the gelatin in cold water. After 5 minutes, drain it and add it to the warm cream. Mix well. Stir the cream every 10 minutes until completely cooled.
• Mix the whipping cream with a tablespoon of vanilla sugar until firm. Incorporate the whipped cream into the caramel with upward movements.

Chocolate Icing:

• Hydrate the gelatin in cold water.
• Place the whipping cream, water, sugar, and syrup over a medium heat. When the syrup is completely smooth, add the broken chocolate pieces. Stir until the chocolate is melted. Turn off the heat. The icing should not boil.
• Add the gelatin and stir well. Let the icing cool and harden. It will be ready to use after 2-3 hours.

Assembly:

• Place one of the cake pieces on a platter. Spread a third of the caramel cream (cooled) on top. Continue layering with the cake, cream, cake, cream, cake. Refrigerate for 1-2 hours.
• Remove the cake from the fridge and cut into rectangles. Place them on a baking rack. Glaze each rectangle with chocolate icing. Transfer the pieces to a platter and refrigerate, allowing the icing to set.
• When serving, decorate the cake with pieces of caramelized sugar.

Enjoy!