01 - Melt dark chocolate gently using a heatproof bowl set over simmering water or in short intervals in the microwave. Coat silicone dome molds (3-inch diameter) with a thick, even layer of melted chocolate using a pastry brush or spoon. Chill molds for 10 minutes to set, then apply a second layer for durability. Refrigerate until completely set, about 30 minutes.
02 - Soften gelatin in cold water—either soak leaves for 5 minutes or bloom powdered gelatin in 2 tablespoons cold water. In a mixing bowl, combine mascarpone, powdered sugar, and vanilla. In another bowl, whip heavy cream to soft peaks, then gently fold into mascarpone mixture. Warm gelatin until dissolved and blend it into the mousse. Pipe or spoon mousse into chilled chocolate shells, filling nearly to the top, and smooth the surface. Refrigerate until fully set, at least 3 hours.
03 - Carefully release set domes from the silicone molds and place them on a wire rack set over a tray.
04 - Soften gelatin in 3 tablespoons cold water. In a saucepan, combine water, sugar, heavy cream, and sifted cocoa powder. Bring to a simmer while whisking until smooth. Remove from heat and cool to approximately 122°F. Stir in softened gelatin until fully dissolved. Allow glaze to cool to 90°F, ensuring optimal pouring consistency.
05 - Pour the cooled mirror glaze evenly over each dome, allowing excess to drip off the sides until fully coated. Carefully transfer to dessert plates. Garnish with gold leaf, chocolate curls, or fresh berries as desired. Refrigerate domes for at least 30 minutes to set the glaze before serving.