Preheat the oven to 180°C. Grease a 23cm deep loose-bottomed cake tin with butter and line the base with baking parchment.

Place the chocolate and butter in a large heatproof bowl set over a pan of gently simmering water, ensuring the base of the bowl does not touch the water. Leave until just melted, stirring occasionally. Remove from the heat and allow to cool slightly. Alternatively, melt in the microwave on high in short bursts, stirring between each burst.

In a clean medium bowl, whisk the egg whites with a pinch of salt using an electric whisk on full speed until stiff peaks form.

In a large bowl, whisk the egg yolks with the icing sugar (and vanilla, if using) until pale, thick and fluffy. Place in fridge until ready to use.

Fold the cooled melted chocolate mixture into the egg yolk mixture until smooth. Stir in the ground almonds, chopped hazelnuts and almond liquor.

Gently fold in one-third of the whipped egg whites to loosen the mixture, then carefully fold in the remaining whites, keeping as much air in the batter as possible.

Pour the mixture into the prepared tin and smooth the surface. Bake for 35–40 minutes, until the top is set but the centre still has a slight wobble. Leave the cake to cool completely in the tin before removing. The cake will firm up as it cools.

To make the mascarpone cream, whisk together the mascarpone, icing sugar and vanilla until smooth and softly whipped.

Serve the cake in slices with a generous dollop of mascarpone cream. Dust lightly with icing sugar if desired.