01 - Melt the chopped dark chocolate in a heatproof bowl set over simmering water or by microwaving in short intervals. Use a pastry brush or spoon to apply a generous layer of melted chocolate to silicone dome molds (3–3.2 inch diameter). Chill for 10 minutes to set, then repeat for a thicker shell. Refrigerate until fully set, approximately 30 minutes.
02 - Soften gelatin leaves in cold water for 5 minutes or bloom powdered gelatin in 2 tablespoons cold water. In a separate bowl, whisk together chilled mascarpone, powdered sugar, and vanilla until smooth.
03 - Whip the cold cream to soft peaks. Gently fold the whipped cream into the mascarpone mixture. Warm the gelatin until just dissolved and fold it into the mousse base.
04 - Spoon or pipe the mascarpone mousse into the prepared chocolate shells, filling nearly to the top. Smooth the surface for an even finish. Refrigerate domes for at least 3 hours to set completely.
05 - Carefully unmold the set domes and place them on a wire rack set over a tray for glazing.
06 - Soften gelatin in 3 tablespoons cold water. In a saucepan, combine water, sugar, cream, and sifted cocoa powder. Bring to a simmer while whisking until smooth. Remove from heat and allow to cool slightly to 122°F. Stir in softened gelatin until fully dissolved. Cool glaze to about 90°F for optimal pouring consistency.
07 - Pour chocolate mirror glaze evenly over each dome, letting excess drip off to fully coat. Use a spatula to remove any drips. Transfer domes to serving plates. Decorate with gold leaf, chocolate curls, or fresh berries as desired. Refrigerate domes for at least 30 minutes before serving to set the glaze.