Chocolate cremeux (the day before) 

1. Melt the chopped dark chocolate using a double boiler.
2. Heat the heavy cream and whole milk in a saucepan until it simmers.
3. Meanwhile, whisk the egg yolks with the sugar using an electric mixer for 1-2 minutes.
4. Incorporate the mixture of hot cream and milk and whisk until you obtain a homogeneous mixture.
5. Transfer the mixture back to the saucepan and cook the custard over medium heat while continuously stirring with a wooden spoon. Check the temperature, which should reach a maximum of 85°C (185°F), until the custard coats the back of the spoon.
6. Then, pour the hot custard over the melted chocolate and vigorously stir to incorporate, creating a smooth and homogeneous mixture.
7. Use an immersion blender if necessary to further smooth the chocolate custard, then pour it into the insert mold.
8. Place the insert mold with the chocolate custard in the freezer for at least 4 hours (or overnight). It should be completely frozen for assembling the log.

Make the brownies

1. Preheat the oven to 175°C (350°F) and prepare a square brownie pan by lining it with parchment paper.
2. Melt the chocolate and butter using a double boiler.
3. In a large bowl, whisk together the eggs and sugar, then incorporate the melted chocolate and butter mixture.
4. Add the dry ingredients, the flour, unsweetened cocoa powder, and a pinch of salt, and gently mix to incorporate them, creating a homogeneous batter.
5. Pour the brownie batter into the prepared pan and bake in the oven for approximately 25 minutes.
6. Allow the brownie to cool completely in its pan before carefully unmolding it.
7. Cut the brownie to obtain a large rectangle that is 1 cm narrower than the log mold.

Milk chocolate mousse

1. Melt the chopped milk chocolate using a double boiler and let it cool slightly (temperature should be a maximum of 50°C or 122°F).
2. In a large bowl, place the cold heavy cream and whip it with an electric mixer for about 2 minutes until you have whipped cream that is not too firm.
3. Gently fold the whipped cream into the melted milk chocolate using a spatula until you have a homogeneous mixture.

White chocolate mousse

1. Rehydrate the half-sheet of gelatin in a bowl of cold water for approximately 5 minutes.
2. Meanwhile, heat 1/3 of the cream in a small saucepan over medium heat, bringing it to a simmer only.
3. At the same time, melt the white chocolate using a double boiler.
4. Incorporate the rehydrated gelatin into the hot cream and vigorously stir to melt it.
5. Pour the mixture of hot cream and gelatin over the melted white chocolate and mix to achieve a smooth preparation. (If you have difficulty melting the white chocolate, adding the hot cream and gelatin will help it melt faster.)
6. Let the mixture of melted white chocolate cool slightly.
7. Meanwhile, whip the remaining heavy cream until it becomes thick whipped cream.
8. Fold the whipped cream into the melted chocolate mixture and gently mix with a spatula until you have a homogeneous but slightly liquid mixture (this is normal).

Log assembly

1. Pour into the bottom of the log mold and smooth it with a spatula to fill the mold completely, filling any gaps and ensuring a smooth, flawless log.
2. Place the frozen chocolate cream insert in the center of the log mold on top of the milk chocolate mousse.
3. Pour the white chocolate mousse and spread it evenly in the log mold until it completely covers the chocolate cream.
4. Add the brownie and lightly press it into place in the mold.
5. Smooth it if necessary with a spatula to have a smooth surface.
6. Place the chocolate log in the freezer for at least 4-6 hours until it is completely frozen.

Mirror glaze and decoration

• Rehydrate the gelatin sheets in a large bowl of cold water for approximately 10 minutes.
• In a saucepan, heat all the ingredients except the cocoa - sugar, glucose syrup, heavy cream, and water - until it comes to a boil.
• Add the gelatin sheets and stir to melt and incorporate them.
• Add the unsweetened cocoa powder and mix to incorporate it.
• Use an immersion blender to smooth the mirror glaze, or strain it through a sieve to achieve a smooth texture.
• Let the cocoa glaze cool to 35°C (95°F).
• Remove the log from the freezer and carefully unmold it, then place it on a rack or position it on two small glasses over a large baking dish to catch the dripping glaze.
• Pour the cocoa glaze over the entire log to cover it completely.
• Gently run a spatula along the edges of the log, then transfer it carefully to a large serving platter.
• Decorate the three chocolate log with star and tree-shaped meringues and place it in the refrigerator to thaw gently for 3-4 hours before serving.