1. Prepare the Salted Caramel Insert

1. Sprinkle the gelatin over the cold water and let it bloom for 5–10 minutes.
2. Heat the sugar in a saucepan over medium heat until it melts into a deep amber caramel.
3. Carefully add the warm heavy cream while stirring continuously.
4. Add the butter and sea salt. Stir until smooth.
5. Remove from the heat and mix in the bloomed gelatin until fully dissolved.
6. Pour the caramel into a small silicone insert mold or a lined container.
7. Freeze for at least 3–4 hours, or until completely firm.

2. Make the Hazelnut Biscuit

1. Preheat the oven to 180°C (350°F). Line a baking tray with parchment paper.
2. Whisk the eggs with the hazelnut flour and sugar until pale and slightly thick.
3. Gently fold in the all-purpose flour and melted butter.
4. In a separate bowl, beat the egg white with the remaining sugar until soft peaks form.
5. Fold the whipped egg white gently into the hazelnut mixture.
6. Spread the batter evenly onto the prepared tray.
7. Bake for 10–12 minutes, until lightly golden and springy to the touch.
8. Let cool completely, then cut a circle slightly smaller than your entremet mold.

3. Prepare the Crunchy Hazelnut Praline Layer

1. Melt the milk chocolate gently in a heatproof bowl.
2. Stir in the hazelnut praline paste until smooth.
3. Add the feuilletine flakes and a pinch of sea salt.
4. Mix gently until all the crispy flakes are coated.
5. Spread the mixture evenly over the cooled hazelnut biscuit.
6. Refrigerate until firm.

4. Make the Chocolate Hazelnut Mousse

1. Bloom the gelatin in the cold water for 5–10 minutes.
2. Heat the milk in a saucepan until steaming but not boiling.
3. Whisk the egg yolks and sugar in a separate bowl until combined.
4. Slowly pour the warm milk over the yolk mixture while whisking.
5. Return everything to the saucepan and cook over low heat, stirring constantly, until slightly thickened and coating the back of a spoon. Do not boil.
6. Remove from the heat and stir in the bloomed gelatin.
7. Pour the hot custard over the chopped dark chocolate. Let stand for one minute, then blend or stir until smooth.
8. Mix in the hazelnut praline paste.
9. Let the chocolate mixture cool to approximately 30–32°C (86–90°F).
10. Whip the cold heavy cream to soft peaks.
11. Gently fold the whipped cream into the chocolate mixture in two or three additions.

5. Assemble the Entremet

1. Pour about half of the chocolate hazelnut mousse into a silicone entremet mold.
2. Use a spatula to push the mousse gently up the sides, removing any large air pockets.
3. Place the frozen salted caramel insert in the center.
4. Cover with the remaining mousse, leaving enough space for the biscuit and praline base.
5. Place the biscuit with the crunchy praline layer facing down onto the mousse.
6. Press gently until the base is level with the mold.
7. Smooth the surface, cover, and freeze for at least 8 hours, preferably overnight.

6. Prepare the Chocolate Mirror Glaze

1. Bloom the gelatin in the cold water for 5–10 minutes.
2. Combine the sugar, glucose syrup, and water in a saucepan.
3. Heat until the mixture reaches 103°C (217°F).
4. Remove from the heat and stir in the sweetened condensed milk.
5. Add the bloomed gelatin and mix until completely dissolved.
6. Pour the hot mixture over the chopped dark chocolate.
7. Let stand for one minute, then blend with an immersion blender, keeping the blade submerged to avoid creating air bubbles.
8. Strain the glaze through a fine sieve.
9. Let it cool to approximately 32–35°C (90–95°F) before using.

7. Glaze the Entremet

1. Remove the entremet from the freezer and carefully unmold it while completely frozen.
2. Place it on a wire rack over a tray to catch excess glaze.
3. Pour the mirror glaze evenly over the top and sides in one continuous motion.
4. Allow the excess glaze to drip off.
5. Carefully transfer the entremet to a serving plate using a cake lifter or spatulas.

8. Decorate and Serve

1. Decorate the top with chopped roasted hazelnuts, chocolate curls, and whole hazelnuts.
2. Add a small piece of edible gold leaf for an elegant finish, if desired.
3. Transfer the entremet to the refrigerator and let it thaw for approximately 6–8 hours before serving.
4. Use a warm, dry knife to cut clean slices, wiping the blade between cuts.