Set up a double boiler with a heat-safe glass bowl that fits over a small pot on the stove. The glass bowl shouldn’t touch the water.
Heat about an inch of water in the pot over medium heat. Place half the chocolate wafers into a heat-safe glass bowl and place it on top of the pot.
Stir the chocolate with a silicone spatula as the chocolate melts. Do not allow the chocolate to get too hot or it will scorch.
Remove from heat as soon as chocolate is half melted.
Continue stirring until all of the chocolate melts. Then add the remaining chocolate and stir until melted.
Once the chocolate has cooled to 82 degrees F, place the bowl back on the double boiler until smooth enough to paint into the mold. Keep chocolate between 82°F and 90°F while working, if possible.
Use a food paint brush to cover the inside of each sphere. Place the mold in the refrigerator for 5 minutes.
Remove the chocolate shells from the mold.
Place half of the molds, cup facing up, on a flat surface. Fill with 1 tablespoon hot cocoa and 1 tablespoon mini marshmallows.
Heat a small pan over low heat on the stove then turn it off. Quickly melt the rim of the unfilled mold on the pan then stick it to the filled mold to adhere them together. Working quickly, do this for all spheres.
To complete, drizzle melted chocolate over the tops of your spheres and decorate with sprinkles. Change the color of the drizzle by adding a drop of food coloring.
To serve: Steam or microwave 8 ounces of milk. Place one hot chocolate bomb in a mug and pour the steamed milk over the top to melt the chocolate. Stir and enjoy.