01 - Melt the semisweet or dark chocolate in a heatproof bowl over simmering water or in 30-second microwave intervals, stirring until smooth.
02 - Using a pastry brush or spoon, coat inside of silicone half-sphere molds evenly with melted chocolate; refrigerate for 10 minutes. Apply a second coat and chill until firm.
03 - Carefully unmold chocolate half-spheres and fill half with 1 tablespoon cocoa mix, 3 mini marshmallows, and a sprinkle of crushed peppermint candies.
04 - Warm a plate in the microwave, press rim of empty half-sphere onto the plate briefly to melt the edge, then seal atop filled half-sphere; smooth seam gently. Repeat for remaining spheres.
05 - Drizzle melted white chocolate over the assembled bombs and sprinkle with extra crushed peppermint candies. Allow to set thoroughly.
06 - Place one cocoa bomb in a mug; pour 1 cup hot milk over it and stir until fully melted before enjoying.