01 - Melt dark chocolate in a heatproof bowl set over gently simmering water, or microwave in short increments until smooth. Coat silicone dome molds (approximately 3-inch diameter) with a generous layer of melted chocolate using a pastry brush or spoon. Refrigerate for 10 minutes to set, then repeat to ensure sturdiness. Chill until completely firm, about 30 minutes.
02 - Soften gelatin leaves in cold water for 5 minutes, or bloom powdered gelatin in 2 tbsp cold water. In a large mixing bowl, whisk together mascarpone, powdered sugar, and vanilla until smooth. Whip heavy cream to soft peaks and gently fold into mascarpone mixture. Gently warm the gelatin until fully dissolved, then incorporate into mousse. Spoon or pipe mousse into prepared chocolate shells, filling nearly to the top. Smooth the surface. Refrigerate for at least 3 hours until firmly set.
03 - Carefully remove set domes from silicone molds. Arrange on a wire rack over a tray to catch excess glaze.
04 - Soften gelatin in 3 tbsp cold water. In a saucepan, blend water, sugar, heavy cream, and sifted cocoa powder. Simmer over gentle heat, whisking until completely smooth. Remove from heat and allow to cool slightly (to about 122°F). Add softened gelatin, stirring until fully dissolved. Let glaze cool to approximately 90°F for ideal pouring consistency.
05 - Pour mirror glaze in an even motion over each dome, allowing excess glaze to drip off for full coverage. Transfer domes onto dessert plates. Garnish with edible gold leaf, chocolate curls, or fresh berries if desired. Chill for at least 30 minutes before serving to set the glaze.