Preheat your oven to 350°F (180°C). Grease a 9-inch springform pan and line both the bottom and sides with parchment paper.

Place the eggs, brown sugar, granulated sugar, and vanilla into a large mixing bowl. Beat with an electric mixer for about four minutes until pale, thick, and fluffy.

Sift together the flour, cocoa powder, baking powder, espresso powder, and salt before adding them to the egg mixture.

Gradually add the dry ingredients to the egg mixture and fold in the melted dark chocolate.

Pour the batter into the prepared pan and smooth the surface. Bake for 15 to 20 minutes until the center springs back when touched and a toothpick comes out with a few moist crumbs.

Cool the sponge completely before adding the mousse.

Pour the lemon juice into a small bowl and sprinkle the gelatin over it. Let it sit for several minutes.

Blend the raspberries until smooth and strain through a fine mesh sieve to remove the seeds.

Combine the raspberry puree with sugar in a saucepan, cook until the sugar dissolves, remove from heat, and stir in the softened gelatin.

Allow the mixture to cool to room temperature before whipping the cold heavy cream until soft peaks form.

Fold the cooled raspberry mixture gently into the whipped cream.

Pour the raspberry mousse over the cooled chocolate sponge in the springform pan and smooth the surface.

Cover the pan and refrigerate for at least three hours, preferably overnight.

Decorate with fresh raspberries and dark chocolate shavings before serving.