Heat the milk chocolate in a microwave-safe bowl for 30 seconds, then stir and continue in 15-second bursts, stirring between each burst. Stop when stirring produces a smooth, melted coating without unmelted pieces.

For the stovetop alternative, melt the milk chocolate in a double boiler instead of using the microwave. The finished chocolate should flow smoothly enough to spread inside the molds.

Spread chocolate over the entire interior of each half-sphere cavity using a spoon back or pastry brush, then freeze for 5 minutes. The first coat should cover the curved walls and rim and feel firm before the next coat.

Brush on a second coat, giving the sides and rims extra attention, then freeze until firm, about 5 more minutes, repeating coating and firming wherever holes or thin patches remain. A continuous, opaque shell with substantial edges will release more readily than a translucent one.

Peel the molds gently away from the firm shells, settle half the shells in cupcake cups, and add 1 tablespoon hot cocoa mix, marshmallows, and any desired additional filling to each supported half. The liners should hold the shells upright with their rims clear for joining.

Heat a microwave-safe plate in the microwave for 90 seconds, then lightly rotate the rim of an empty half against it and immediately join that half to a filled one. The softened edge should sit flush against the lower shell to form a closed sphere.

Work melted chocolate from the plate into any remaining seam gaps with a butter knife. The join should look continuous, with no openings where cocoa powder can escape.

Add the melted dark chocolate in thin drizzles and finish with extra mini marshmallows or your preferred decorations. The drizzle should cross the shell’s surface without obscuring its shape.

Set a finished bomb in a mug, pour very hot milk or hot water over it, and stir to combine. The shell and cocoa mix should dissolve into the liquid as the marshmallows rise.