Opera cake with hazelnut praline ice cream

Warm the milk, cream, trimoline, milk powder and glucose powder to 50°C. Add in the stabiliser and bring to a simmer

Whisk a little of the hot milk mixture into the egg yolk. Slowly pour the rest of the mixture onto the egg yolk, whisking constantly. Transfer everything back to the pot and cook, whisking constantly, until it reaches 82°C

Blend in the hazelnut praline and then chill completely in the fridge. Once cool, churn in an ice cream machine. Transfer to the freezer to set

For the cocoa nib tuile, heat up the sugar, milk, glucose and butter to 100°C, stirring constantly. Take the pan off the heat and stir in the cocoa nibs and cocoa powder

Line an oven tray with parchment paper and pour the tuile batter onto the tray - it should be about 0.5 cm thick

Allow the tuile to cool and then freeze it

Preheat the oven to 160°C

Sieve together all of the dry ingredients for the sour cream sponge

Use an electric whisk to cream together the butter, sugar and vanilla extract. Whisk the eggs into the butter and sugar mixture, little by little

Once the eggs are incorporated, add the flour mixture and the sour cream in alternating spoonfuls, about a third of each at a time.

Grease and line the three 15 cm square trays. Divide the cake batter between the three trays equally, spreading it out to the edges

Bake the cake for 14 minutes, or until the sponge springs back when pressed lightly. Once cooked, transfer to a cooling rack and allow to cool completely

For the chocolate crémeux, first mix together the cream, sugar, milk and egg yolk. Warm the cream mixture in a bain-marie until it reaches 82°C, then remove from the heat

Whisk the chocolate into the warm cream until smooth, then set aside to cool

For the hazelnut buttercream, first whisk together the egg white and sugar. Warm the mixture in a bain-marie to 55°C. You will need to whisk it constantly, and be careful that the bottom of the bowl doesn't get too hot or the egg whites might cook a little and become grainy

Take the egg whites and sugar off the heat, and whisk until it cools down to room temperature and forms stiff peaks

If using a stand mixer, switch to the paddle attachment. Add the butter to the meringue, piece by piece, while it's running. Once all the butter is incorporated, beat in the praline and season with salt to taste and set aside

Use the 12 cm square pastry frame to cut out each sponge. Place the frame on a lined tray and add the first layer of sponge cake. Brush the sponge with coffee liqueur

Add 200g crémeux and spread it out over the sponge. Add in another layer of cake and then brush it with coffee liqueur

Add 300g of the hazelnut buttercream onto the second sponge layer and top it with the final piece of sponge cake

Brush the final layer with more coffee liqueur and then top it with 40g of crémeux. Place in the fridge and allow to set, and transfer the rest of the crémeux to a piping bag

Preheat the oven to 170°C

Transfer the frozen tuile to a silpat mat, removing the parchment paper. Cook in the oven for 5–7 minutes, or until the mixture stops bubbling

Remove from the oven but don't turn off the oven. Allow to cool slightly, then cut out into 4cm discs

Lightly toast the hazelnuts in the oven until golden brown, then cut them all in half except for three or four

Remove the mould from the set opera cake (lightly blow torching the outside of the mould can help release it) and cut into 6 × 3 cm wide portions

Place a tuile on top of each piece of opera cake, pipe some crémeux on one half, and microplane the whole toasted hazelnuts on top of the crémeux. Scatter a few hazelnut halves and cocoa nibs on top of the cake. Place a rocher of ice cream on top of the tuile next to the crémeux, and sprinkle with more cocoa nibs