01 - Preheat oven to 350°F. Line an 8-inch springform pan with parchment paper and set aside.
02 - In a mixing bowl, whisk together flour, cocoa powder, baking powder, sugar, and salt. In a separate bowl, combine eggs, melted butter, and vanilla extract. Fold wet ingredients into dry mixture just until incorporated. Spread batter evenly into the prepared pan.
03 - Bake for 20 to 25 minutes until a toothpick inserted in the center comes out clean. Allow the cake to cool completely in the pan.
04 - Soften gelatin sheets in cold water. In a saucepan, combine raspberries, sugar, and water, cooking over medium heat until the berries break down. Blend until smooth, then strain through a sieve to remove seeds. Warm the strained puree gently 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 dark chocolate using a double boiler or microwave in 30-second intervals, stirring between each. Let cool slightly until lukewarm.
06 - Beat egg yolks with 2 tablespoons of sugar and vanilla extract until pale and thick. Fold in the melted chocolate until fully combined.
07 - In a clean, grease-free bowl, whip egg whites with a pinch of salt until soft peaks form. Gradually add the remaining 2 tablespoons of sugar and continue beating to stiff, glossy peaks.
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 in two additions, preserving as much volume as possible, until smooth and airy.
10 - Pour the chocolate mousse over the set raspberry layer, smoothing the top with a spatula. Cover with plastic wrap and refrigerate for at least 4 hours or until completely set.
11 - Release the cake from the springform pan. Arrange fresh raspberries on top, add chocolate curls, and dust lightly with confectioners' sugar if desired. Slice with a warm knife for clean portions.