• Chop chocolate chips as finely as possible, which will aid in more even melting.
• Place 5 ounces of chopped chocolate (about ⅔ of the chocolate) in a microwave-safe bowl. Microwave on the defrost setting in 15-second increments, stirring between each. When most of the chocolate is melted, with a few pieces still solid, stop microwaving and stir to finish melting the chocolate. The temperature for semi-sweet chocolate should be between 100 to 113°F at this point and not hotter than 120°F.
• Add the remaining chocolate pieces and stir until they are mostly melted and incorporated. Continue stirring the chocolate until it cools to about 85°F.
• Place the chocolate back into the microwave on the defrost setting for 15 seconds once more. This should be enough time to heat the chocolate back up to 90°F and make it fluid for molding.
• Use a paintbrush or the back of a spoon (a soup spoon works great) to coat the inside of each sphere of the candy mold. Apply two thin coats or one thicker coat, between 1/16-inch and ⅛-inch thickness.
• Use a knife or straight edge to clean up any excess chocolate on the surface of the mold.
• Place the mold in the refrigerator for 3 to 5 minutes until the chocolate sets.
• Gently pop the molded chocolate from the silicone mold.
• Spoon 1½ teaspoons of hot cocoa mix powder into one side of each sphere half. Add as many mini marshmallows as you can.
• Heat an empty plate in the microwave for about a minute and place it next to your work space. 
• Place the empty half of each sphere, open side down, onto the plate for just a couple of seconds to melt the rim. Quickly press the melted rim against the rim of the other half to seal the sphere together.
• You can alternately paint a bit of melted chocolate on the edge to glue the two sides together, but this leaves more of a visible line.
• Place white chocolate chips in a piping bag or Ziploc bag. Microwave in 20-second increments, squishing the chocolate within the bag until it is fully melted. Snip off a small corner of the bag (or the tip if using a piping bag).
• Drizzle the white chocolate over the top of each hot chocolate sphere for decoration.

Serving

• To serve, place a hot chocolate bomb in a mug. Pour 8 ounces of steamed milk over the chocolate. Stir and drink up!