Chocolate Hazelnut Bars

MAKE THE CHOCOLATE COFFEE WAFER BASE
Preheat oven to 350°F (175°C). Line a 9 x 13-inch (23 x 33 cm) pan with parchment paper, leaving a 2-inch overhang on the long sides for clean removal. In a food processor, pulse the flour, cocoa powder, espresso powder, sugar, and salt to combine. Add the cold butter cubes and pulse until the mixture resembles coarse sand with some pea-sized pieces. Add the egg yolk and vanilla and pulse until the dough just begins to clump together. Press the dough firmly and evenly into the bottom of the prepared pan — use the flat bottom of a measuring cup to create a perfectly level, uniform layer. Dock the surface with a fork at regular intervals to prevent bubbling. Bake for 15–18 minutes until the base is firm and dry to the touch but not overbaked. Cool completely in the pan on a wire rack.

MAKE THE SALTED CARAMEL
In a medium heavy-bottomed saucepan, spread the sugar in an even layer. Heat over medium heat, without stirring, until the edges begin to melt and turn amber. Gently swirl the pan to encourage even caramelisation — do not stir with a spoon. Continue until you have a deep amber caramel, about 6–8 minutes total. Remove from heat and carefully pour in the warm cream — it will bubble aggressively. Whisk until smooth, then whisk in the butter, flaky salt, and vanilla. If any lumps formed, return to low heat and stir until dissolved. Allow the caramel to cool for 10 minutes until it thickens slightly but is still pourable, then pour evenly over the cooled wafer base. Use an offset spatula to spread it into a perfectly even layer. Refrigerate for 30 minutes until the caramel is set but not rock-hard.

MAKE THE WHIPPED HAZELNUT GANACHE
Place the finely chopped dark chocolate, hazelnut paste, butter, and espresso powder (if using) in a heatproof bowl. In a small saucepan, heat half the cream (½ cup / 120 ml) until it just begins to simmer. Pour the hot cream over the chocolate mixture and let stand for 2 minutes, then stir gently from the centre outward in small circles until completely smooth and glossy. Allow to cool to room temperature, about 20 minutes. In a separate bowl, whip the remaining cold cream (½ cup / 120 ml) to medium-soft peaks. Fold one-third of the whipped cream into the chocolate-hazelnut mixture to lighten it, then gently fold in the remaining whipped cream until just combined — the texture should be mousse-like, light yet rich.

ASSEMBLE THE LAYERS
Spread the whipped hazelnut ganache evenly over the set caramel layer using a clean offset spatula. Start with a large dollop in the centre and spread outward toward the edges in smooth, confident strokes. Level the top by holding the spatula at a low angle and drawing it across the surface in a single motion. Refrigerate for at least 1 hour, or until the ganache is firmly set.

APPLY THE CHOCOLATE GLAZE
Melt the dark chocolate and coconut oil together in a heatproof bowl set over barely simmering water (or in 20-second microwave bursts, stirring between each). Stir until completely smooth and glossy. Allow to cool for 3–4 minutes until fluid but not hot. Pour the glaze over the set ganache layer and spread quickly and evenly with a clean offset spatula — the cold ganache will begin to set the glaze almost immediately. Before the glaze sets fully, scatter the chopped toasted hazelnuts evenly across the surface and finish with a light scattering of flaky sea salt. Refrigerate for 30 minutes until the glaze is completely set.

CUT INTO BARS
Using the parchment overhang, lift the entire slab out of the pan and onto a cutting board. Heat a sharp chef's knife by running it under very hot water, then dry it thoroughly. Use a ruler to mark even cuts — for 16 bars, cut into a 4 x 4 grid. Press the warm knife down through the layers in a single, firm motion rather than sawing. Wipe and reheat the blade between every cut.

SERVE
Allow the bars to come to cool room temperature for 10–15 minutes before serving. The wafer base will have a slight chew, the caramel will be yielding but not runny, the ganache will be mousse-soft, and the chocolate glaze will provide a satisfying snap.