Grease and line the base and sides of a 23cm (9-inch) springform pan, then preheat your oven to 180°C (350°F).

In a medium bowl, combine the eggs, light brown sugar, granulated sugar, and vanilla extract. Whip on medium-high speed until light and creamy, about 4 minutes.

Sift the flour, cocoa powder, baking powder, espresso powder, and salt into the egg mixture. Mix on low speed until just a few flour streaks remain.

Fold in the melted chocolate with a rubber spatula until everything is smooth.

Pour the batter into the prepared springform pan, tap the pan to release air bubbles, and bake for 15-20 minutes until the center springs back. Allow to cool to room temperature.

In a small bowl, mix the lemon juice and powdered agar-agar, letting it sit for a few minutes to soften.

Blend the fresh raspberries until smooth, then strain the puree through a fine mesh sieve into a saucepan, removing the seeds.

On medium-low heat, add granulated sugar to the raspberry puree and simmer. Add the agar-agar mixture and heat gently, stirring until dissolved. Remove from heat and let cool for about 20 minutes.

In another bowl, whip the cream until soft peaks form, then slowly mix in the cooled raspberry puree until combined.

Pour the raspberry mousse over the cooled chocolate sponge in the springform pan. Smooth the top, cover, and refrigerate for at least 3 hours, preferably overnight.

Carefully release the cake from the pan, garnish with fresh raspberries and chocolate shavings, slice with a warm knife, and serve immediately.