01 - Melt dark chocolate in a heatproof bowl set over simmering water or microwave in short intervals until smooth. Using a pastry brush or spoon, coat silicone dome molds (3-inch diameter) with a generous layer of melted chocolate. Chill for 10 minutes to set; repeat for a thicker shell. Chill until completely set, about 30 minutes.
02 - Soften gelatin leaves in cold water for 5 minutes, or bloom powdered gelatin in 2 tablespoons cold water. In a mixing bowl, whisk together mascarpone, powdered sugar, and vanilla. Whip the cream to soft peaks, then gently fold into the mascarpone mixture. Gently heat gelatin until dissolved, then fold into the mousse base. Spoon or pipe the mousse into chocolate shells, filling nearly to the top, then smooth the surface. Refrigerate for at least 3 hours to set.
03 - Carefully remove the set domes from silicone molds and place on a wire rack positioned over a tray.
04 - Soften gelatin in 3 tablespoons cold water. In a saucepan, combine water, granulated sugar, heavy cream, and sifted cocoa powder. Bring to a simmer over medium heat, whisking until perfectly smooth. Remove from heat and cool slightly to 122°F. Stir in softened gelatin until fully dissolved. Cool further to 90°F to reach ideal pouring consistency.
05 - Pour mirror glaze evenly over each dome, coating completely and allowing excess to drip off. Place domes onto dessert plates. Decorate with gold leaf, chocolate curls, or fresh berries as desired. Refrigerate domes for 30 minutes before serving to allow glaze to set.