Start by setting up a double boiler. You’ll need a pot filled with water that's brought to a gentle simmer. Move your oven rack to the middle position and preheat your oven to 400°F. Take an 18" x 13" jelly roll pan, and line it with parchment paper, making sure to grease it lightly for easy removal later.

In a metal mixing bowl, combine the 3 large eggs, 3 large egg yolks, ¾ cup of evaporated cane sugar, and a pinch of salt. Mix these ingredients slightly before placing the bowl over your simmering water. Keep whisking until the mixture feels lukewarm and reaches about 100°F. It's important to get it warm without cooking the eggs.

Once heated, remove this bowl from the heat and attach it to your mixer with a whisk attachment. Beat the mixture for roughly 5 minutes until it triples in volume and transforms into a pale yellow color. The ribbons of the batter should fall back into the bowl smoothly.

Next, sift the ½ cup of cake flour and ¼ cup of cornstarch into the egg mixture in three parts, folding gently with a spatula after each addition to avoid deflating the eggs. Once smoothly combined, pour the batter into the prepared jelly roll pan, spreading it evenly. Bake it in the preheated oven for 7-10 minutes. Keep an eye on it; when a knife comes out clean, it’s ready.

After baking, let the cake cool by sliding it onto a wire rack directly, ensuring it cools evenly without the pan restricting airflow.

While your cake cools, you can start on the chestnut puree. Slice the vanilla bean lengthwise and scrape out the seeds. Combine the seeds with ½ cup of heavy cream, ½ cup of evaporated cane sugar, and 1 large egg yolk in a small saucepan. Heat this mixture over low heat while whisking, allowing it to thicken. Keep stirring to prevent the eggs from scrambling.

Once it thickens slightly, remove it from heat and let the flavor of the vanilla bean steep while it cools. When cooled, process this mixture with the 425 grams of unsweetened chestnut puree in a food processor until smooth and creamy. Strain the puree through a double mesh strainer for a finer texture, then cover and set aside.

In the bowl of your clean electric mixer, add ¾ cup of heavy cream. Whip it using the whisk attachment until soft peaks begin to form. Gradually add the 3 tablespoons of powdered sugar and continue whipping until fully integrated. Carefully fold in ⅓ cup of the prepared chestnut puree, making sure not to overmix, so you maintain those lovely peaks.

Once the genoise has completely cooled, carefully separate it from the parchment paper and trim off any hardened edges. Cut out eight rectangles measuring about 2" x 1.5". These will be your individual servings.

Now, take a pastry bag fitted with a large round tip and fill it with the chestnut cream. Pipe three layers of cream onto the top of each cake, making each layer progressively smaller to create that barn-roof shape.

For the finishing touch, fill another pastry bag with the chestnut puree using a medium round tip. Begin piping from the bottom corner of one of the cakes. In a continuous motion, flow the puree over the top, circling around to cover the sides until you create a beautiful dome. If for some reason the line breaks, don’t stress! You can start again from the point it broke to complete your design.