• See the steps with images in the article and read my tips before starting.

Chocolate sponge cake :

• Cut out 2 rectangles for 2 logs. Wrap a rectangle in plastic wrap and freeze it for later use.
• You can use the soft biscuit as I usually do, it's better than sponge cake.
• Preheat oven to 180°C (350°F )
• Whisk the eggs with the sugar and vanilla sugar until they whiten and triple in volume. Use a Kitchenaid-type stand mixer or an electric hand mixer.
• Add the sifted flour and cocoa mixture in three stages. Mix gently with a spatula or whisk, working in circles from the center outwards. Do not whisk to avoid deflating the batter.
• Spread the batter onto a baking tray lined with parchment paper, forming a 25 x 20 cm (9.8 x 7.9 inches) square.
• Bake for 12 minutes more or less. The sponge should not dry out, so keep an eye on the baking towards the end. A skewer inserted into the center should come out clean.
• Remove from the baking tray and leave to cool, covered with a towel.
• Once cooled, carefully remove the parchment paper and trim the edges of the sponge to remove any dry parts. Then, cut two rectangles slightly smaller than the dimensions of the mold. I cut it to 24 cm by 8.5 cm (9.4 x 3.3 inches), which is slightly smaller than the mold (25 x 9 cm / 9.8 x 3.5 inches).
• Wrap the extra sponge in plastic wrap and freeze it, while covering the one you'll be using with a towel.
• If you want to use a praline crunch, spread it over the sponge and let it set in the refrigerator.

The whipped cream for the 3 mousses

• Whip the entire cream and divide it into 3 equal portions to make the chocolate mousses.
• In the cold bowl of the stand mixer, pour the very cold heavy cream and whip it at medium speed. As soon as many bubbles have formed, increase the mixer speed to maximum.
• You should achieve a soft whipped cream that holds slightly on the whisk but is not stiff enough to pipe.
• Weigh the cream and divide it into 3 equal portions, placing each in a separate bowl. 100 g x 3 (3.5 oz x 3) in my case. Set aside in the refrigerator.

White chocolate mousse

• Rehydrate the gelatin in a bowl of very cold water. It should be well covered with water.
• Melt the white chocolate in the microwave or using a double boiler.
• Heat the milk and remove it from the heat just before it boils to prevent the milk skin from forming.
• Add the squeezed-out gelatin and stir to dissolve it.
• Pour the hot milk over the melted chocolate in two parts to create a smooth "ganache" emulsion.
• If the ganache is cold, gently heat it in a double boiler. This will prevent the mousse from becoming too firm and from being easy to pipe. It should be warm, comfortable to the touch, not hot.
• Add a little cream to the ganache and mix without being careful.
• Gently fold this ganache into the remaining cream in 2 batches, stirring with a spatula from bottom to top.
• Pour the white chocolate mousse into the Yule log mold and tap it on the countertop to spread it evenly. Freeze for 25 minutes more or less. The mousse should be set on top before pouring the second mousse over it.

Milk chocolate mousse

• Rehydrate the gelatin in a bowl of very cold water. It should be well covered with water.
• Melt the milk chocolate in the microwave or using a double boiler.
• Heat the milk and remove it from the heat just before it boils to prevent a milk skin from forming.
• Add the squeezed-out gelatin and stir to dissolve it.
• Pour the hot milk over the melted chocolate in two parts to create a smooth "ganache" emulsion.
• If the ganache is cold, gently heat it in a double boiler. This will prevent the mousse from becoming too firm and from being easy to pipe. It should be warm, comfortable to the touch, not hot.
• Add a little cream to the ganache and mix without being careful.
• Gently fold this ganache into the remaining whipped cream in 2 batches, mixing from bottom to top with a spatula.
• You can do the opposite and add all of the whipped cream in three parts to the ganache.
• Pour the milk chocolate mousse into the Yule log mold over the set white chocolate mousse and tap it on the countertop to spread it evenly. Place it back in the freezer to firm up for about 25 minutes, more or less.

Dark chocolate mousse

• Proceed in the same way as for the previous mousse preparations.
• Pour the dark chocolate mousse over the set milk chocolate mousse. Tap the mold on the countertop to spread it evenly.
• Place the sponge cake or soft biscuit on top, whichever you have chosen to make according to your taste.
• Gently press down on it to push the mousse up the sides. The biscuit will be hidden when unmolding. Smooth with a small offset spatula.
• Cover the mold with plastic wrap and return it to the freezer for at least 8 hours. It's best to prepare it the day before or in the morning for the evening. For easy unmolding, the mousses must set.

The next day

• If you choose to glaze the log, unmold it only once the glaze is ready and at the correct temperature. There are many mirror glazes, you just need to choose the one that suits you.
• I opted for a simple decoration, leaving the log "naked" with the three layers of chocolate mousse visible. I decorated it with white marshmallow stars and tuile cookies made of dark and milk chocolate. These tuiles are crispy because they contain flakes of feuilletine. This compensates for the lack of praliné crunch that I didn't add.
• Let the three-chocolate Yule log thaw slowly in the refrigerator to prevent the formation of water droplets from condensation. Since I was in a hurry, I thawed it for an hour in the refrigerator and the rest of the time at room temperature.
• The yule log is best enjoyed cold, but not frozen like ice cream. The mousses are airy and light.