01 - Place the finely chopped semi-sweet chocolate in a microwave-safe bowl. Heat in 30-second intervals, stirring thoroughly between each, until completely melted and smooth.
02 - Using a pastry brush or the back of a spoon, coat the interior of silicone half-sphere molds (approximately 6 cm diameter) with a layer of the melted chocolate. Chill for 5 minutes. Apply a second layer, ensuring thorough coverage particularly along the edges, and refrigerate until fully solidified, about 10 minutes.
03 - Carefully remove the solidified chocolate half-spheres from the molds and arrange them on a tray lined with parchment paper.
04 - Spoon 1 tablespoon of hot cocoa mix and a generous portion of mini marshmallows into half of the prepared chocolate shells.
05 - Warm a microwave-safe plate briefly. Gently press the empty chocolate half-shells onto the warm plate to slightly melt their edges, then immediately align and press them onto the filled halves to create a seal. Hold for a moment until the seam sets.
06 - If desired, artfully drizzle the melted white chocolate over the sealed hot chocolate bombs. Adorn further with sprinkles or edible glitter. Allow the decorations to set completely.
07 - Place one completed hot chocolate bomb into a mug. Pour 1 cup (240 ml) of very hot milk over the bomb and stir until it has entirely dissolved, revealing a rich chocolate beverage.