WHAT YOU NEED

For the salted caramel inserts
155g liquid glucose
200ml single (pure) cream
50ml full-cream milk
5g salt
Seeds of 1 vanilla bean
95g white (granulated) sugar
70g unsalted butter, cubed

For the espresso mousse
2 gelatine sheets (titanium grade)
135ml full-cream milk
20g freeze-dried coffee granules
45g egg yolks
30g white (granulated) sugar
280g white chocolate
Ice cubes
630ml thickened (whipping) cream
8 salted caramel inserts (see above)

For the brownie base
Oil spray, for greasing
270g 60% dark chocolate
250g unsalted butter
4 eggs
240g white (granulated) sugar
80g dark cocoa powder
60g plain (all-purpose) flour
1 tsp baking powder

For the chocolate glaze
6 gelatine sheets (titanium grade)
290ml water
240ml thickened (whipping) cream
360g white (granulated) sugar
120g dark cocoa powder
75g liquid glucose

For the assembly
16 roasted hazelnuts
Fennel fronds, to garnish
Edible gold dust, to garnish

To make the salted caramel inserts
Combine 50g of the glucose with the cream, milk, salt, and vanilla seeds in a saucepan and bring to a simmer.
Meanwhile, combine the sugar with the remaining 105 g of glucose in another saucepan. Cook over medium–high heat, stirring occasionally, until the mixture turns a deep-brown amber and reaches a temperature of 182°C on a sugar thermometer.
Slowly whisk in the butter until emulsified, then pour in the hot cream mixture and bring to the boil. Cook for 15–20 mins or until the caramel is thick and reduced by a third (don’t overcook or it may split). Set aside until completely cool. If the caramel isn’t firm like a ganache, return it to the heat to reduce further.
Transfer the caramel to a piping bag. Pipe eight 3cm rounds onto a tray lined with baking paper and freeze until solid.

To make the espresso mousse
Soak the gelatine in cold water to soften.
Combine the milk and coffee in a small saucepan and bring to a simmer.
Meanwhile, whisk the egg yolks and sugar in a small heatproof bowl until fluffy. Slowly whisk in the hot milk mixture. Pour the mixture back into the pan and cook, whisking constantly, until the anglaise reaches 84°C on a sugar thermometer. Remove from the heat. Squeeze the excess water from the softened gelatine, add it to the anglaise, and whisk until dissolved and well combined.
Add the white chocolate and stir until melted. Pass the anglaise through a fine sieve into a large metal bowl sitting in an ice bath. Leave to cool to below 25°C.
Whip the cream until medium peaks form. Fold the cream into the cooled anglaise mixture in three batches. Transfer the mousse to a piping bag and pipe it into eight 6.5cm silicone stone moulds, filling them almost to the top.
Press a salted caramel insert into each mould, then add enough mousse to cover the insert and fill the mould. Level the surface, then freeze overnight.

To make the brownie base
Preheat the oven to 170°C. Line a shallow baking tray with baking paper and spray with oil.
Combine the chocolate and butter in a heatproof bowl over a saucepan of simmering water and stir occasionally until melted. Remove from the heat and fold in the eggs.
Sift the sugar, cocoa, flour, and baking powder onto the chocolate mixture and fold until a batter is formed.
Spoon the brownie batter onto the baking tray and spread until it is 1.5cm thick. Bake the brownie for 15–22 mins or until the centre is cooked and not too wet. Cool slightly, then place the brownie in the freezer to cool.
Using a 5cm round cutter, cut eight rounds from the brownie. Place in an airtight container in the fridge or freezer until needed.

To make the chocolate glaze
Soak the gelatine in cold water to soften.
Combine the water, cream, sugar, cocoa, and glucose in a saucepan. Whisk over medium heat until simmering, then remove from the heat. Squeeze the excess water from the softened gelatine, add it to the pan, and whisk until dissolved and well combined.
Using an immersion blender, blend the mixture until glossy. Strain the glaze into a jug and set aside to cool to 28°C.

Assembly
Unmould the frozen mousse rounds and place them on a wire rack with a tray underneath to catch the excess chocolate glaze.
Check the temperature of the chocolate glaze. If needed, gently reheat it in the microwave until it is between 28°C and 30°C.
Pour the glaze over one of the mousse rounds until evenly coated. Using a small spatula, release the glazed mousse from the wire rack and place it on top of one of the brownie circles. Repeat with the remaining mousse rounds. Place each cake on a serving plate.
Halve eight of the hazelnuts, then roughly chop eight of the hazelnut halves. Garnish each cake with a whole hazelnut, a hazelnut half and some chopped hazelnuts. Finish with a sprig of fennel and gold dust.