01 - Preheat oven to 350°F. Line an 8-inch springform pan with parchment paper and set aside.
02 - In a large bowl, whisk together the flour, cocoa powder, baking powder, sugar, and salt. In a separate bowl, combine the eggs, melted butter, and vanilla extract. Pour the wet ingredients into the dry mixture and stir just until combined. Spread the batter evenly into the prepared springform pan.
03 - Bake for 20 to 25 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool completely in the pan.
04 - Soften the gelatin sheets in cold water. In a saucepan, combine the raspberries, sugar, and water. Cook over medium heat until the berries break down completely. Blend the mixture and strain through a fine sieve to remove the seeds. Gently warm the strained puree and dissolve the softened gelatin into it. Let cool to room temperature, then pour over the cooled cake base. Refrigerate until set, approximately 1 hour.
05 - Melt the dark chocolate using a double boiler or microwave in short intervals. Let it cool slightly until lukewarm.
06 - Beat the egg yolks with 2 tablespoons of sugar and the vanilla extract until the mixture turns pale and creamy. Fold in the melted chocolate until fully incorporated.
07 - In a clean, dry bowl, whip the egg whites with a pinch of salt until soft peaks form. Gradually add the remaining 2 tablespoons of sugar and continue beating until stiff, glossy peaks hold.
08 - In a separate chilled bowl, whip the cold heavy cream to soft peaks.
09 - Gently fold the whipped cream into the chocolate mixture. Then delicately fold in the whipped egg whites, working in two additions to keep the mousse light and airy.
10 - Pour the chocolate mousse over the set raspberry layer and smooth the top with a spatula. Cover with plastic wrap and refrigerate for at least 4 hours, or until completely firm.
11 - Release the cake from the springform pan. Arrange fresh raspberries, chocolate curls, and a light dusting of powdered sugar on top before serving.