Preheat oven to 180°C (350°F). Line the base of a 20 cm (8-inch) springform pan with parchment and lightly grease the sides.

In a large bowl, whisk the 3 eggs, light brown sugar, granulated sugar, and vanilla extract together. Beat on high for 6–8 minutes until thick, pale, and ribboning when the whisk is lifted.

Sift together the plain flour, cocoa powder, baking powder, espresso powder, and salt. Fold the dry mix gently into the egg mixture in two additions, keeping as much air as possible.

Fold in the cooled melted dark chocolate until just combined. Avoid over-mixing.

Pour into the prepared pan, smooth the top, and bake for 20–25 minutes until the top springs back slightly and a skewer comes out with a few moist crumbs.

Cool completely in the tin on a wire rack. Once cool, remove from pan and, if needed, level the top so the sponge sits flat.

Place 400 g raspberries and 100 g sugar in a saucepan with the 45 ml lemon juice. Warm gently and stir until the sugar dissolves and berries begin to break down for 3–5 minutes. Remove from heat.

Strain if you want a seed-free mousse. Measure the purée consistency; you want it warm but not piping hot.

Sprinkle the 2¼ tsp powdered gelatine evenly over a few tablespoons of cold water or directly over the lemon juice. Let bloom for 3–5 minutes, then stir into a small amount of the warm purée to dissolve fully, then mix back into the rest of the purée.

Whip the 480 ml cold double cream to soft–medium peaks. Stop when the cream holds a soft peak but is still glossy.

Cool the raspberry + gelatine mixture until it is slightly thickened and just lukewarm. Fold one-third of the whipped cream into the purée to lighten it, then fold in the remaining cream gently until homogenous.

Gently fold in the reserved 125 g fresh raspberries (whole or halved).

Place the cooled sponge in an 8-inch cake ring or the springform base. Pour the mousse over the sponge, smooth the top, and tap the pan gently to release air bubbles.

Refrigerate for at least 4–6 hours, preferably overnight, until fully set.

Once set, remove the ring or release the springform. Decorate with 50 g dark chocolate shavings and extra raspberries before serving.

For neat slices, chill the cake well and wipe a hot knife clean between cuts.