Hazelnut Sponge, Dark Chocolate Mousse, Feuilletine Hazelnut, Guanduja Cream Recipe

Preheat and prepare

Preheat oven to 180°C (350°F). Line a 20 cm (8 in) round cake pan or a rimmed baking sheet with parchment and lightly butter.

In a bowl, whisk together flour, ground toasted hazelnuts and a pinch of salt. Set aside.

In a heatproof bowl set over a bain-marie (or in a stand mixer with whisk), whisk eggs, egg yolk and granulated sugar until the mixture reaches about 38–40°C (100–104°F) or is warm to the touch and volume increases slightly (if using a stand mixer, whisk on medium-high until pale and ribbon stage).

Remove from heat and continue to whisk until the mixture is thick, glossy and has cooled to room temperature (or use the stand mixer until it forms ribbons). Stir in vanilla.

Fold the dry ingredients gently into the egg mixture in two additions, using a rubber spatula to keep as much air as possible. Fold in the melted cooled butter in a thin stream until just combined.

Pour batter into prepared pan, spread evenly and bake 12–15 minutes (for sheet) or 18–22 minutes (for 20 cm round), until the sponge is springy and a toothpick comes out mostly clean. Do not overbake.

Cool on a wire rack. If necessary, trim to fit the molds or rings you will use for assembly (recommend cutting to 20 cm round or dividing into rounds as needed).

If using gelatin: sprinkle gelatin over 15 ml cold water and let bloom for 5 minutes. Gently melt to dissolve and set aside.

Place chopped dark chocolate in a heatproof bowl.

In a small saucepan, combine milk and sugar and bring just to a simmer. In a separate bowl, whisk the egg yolks lightly. Temper the yolks by adding about one third of the hot milk mixture to the yolks while whisking, then return the tempered yolk mixture to the saucepan.

Cook the yolk-milk mixture over medium-low heat, stirring constantly, until it thickens slightly and coats the back of a spoon (do not boil). Remove from heat immediately.

Pour the hot custard over the chopped chocolate and let sit 1–2 minutes, then stir gently until smooth. Add cubed butter and the softened gelatin (if using) and stir until incorporated and glossy. Allow the chocolate base to cool to about 30–35°C (86–95°F).

Whip the chilled heavy cream to soft peaks. Fold one-third of whipped cream into the chocolate base to loosen it, then gently fold in the remaining cream in two additions until homogeneous, keeping the mousse light. Use immediately for assembly or chill briefly to firm slightly.

Place feuilletine (or crushed cookies) in a bowl. Add hazelnut praline paste and stir until evenly coated. If the paste is very stiff, warm it briefly (10–15 seconds) in the microwave to make it spreadable.

Fold in toasted chopped hazelnuts and the melted dark chocolate. The mixture should be cohesive but still crunchy. Chill for 10–15 minutes to set slightly if needed.

Portion the feuilletine mixture to the same diameter as the sponge or use it as a layer between sponge and mousse. Keep chilled until assembly.

Place milk chocolate in a heatproof bowl. In a small saucepan, heat the heavy cream until just simmering, then pour over the chocolate. Let sit 1 minute, then stir until smooth.

Stir in hazelnut paste until fully incorporated and silky. Add butter and sea salt, stirring until butter melts and the mixture is glossy.

Let the gianduja cool to room temperature. If you want a pipeable/softer cream, whip slightly with an immersion blender or hand whisk to incorporate a little air; for a firmer layer, chill until spreadable but not solid.

Prepare a 18–20 cm (7–8 in) removable cake ring or molds lined with acetate if available. Place the hazelnut sponge round into the base.

If using gianduja as a thin layer: spread 6–8 mm of gianduja cream evenly over the sponge. Smooth with an offset spatula and chill 10 minutes to set.

Evenly distribute the feuilletine hazelnut crunch over the gianduja (or directly on the sponge if skipping gianduja layer). Press lightly to create a uniform crunchy layer.

Pipe or spoon the dark chocolate mousse on top of the crunch to a height of about 2–3 cm above the ring, leaving the top smooth. Tap gently to remove air pockets. Smooth the top with an offset spatula or spatula dipped in hot water and wiped dry.

Chill the assembled cake in the refrigerator for at least 3–4 hours or overnight to fully set. If additional stability is needed, freeze for 30–60 minutes before unmolding.

To unmold, run a warm knife around the ring, remove the ring and acetate. Glaze the top with neutral glaze or pour a thin layer of tempered chocolate if desired. Dust edges with cocoa powder and garnish with toasted hazelnuts.

Slice with a knife warmed in hot water and wiped dry for clean slices. Serve chilled or at cool room temperature.