Begin by putting plenty of water in the bottom of your double boiler. When the water is boiling, add the chocolate chips to the top and begin the melting process. The slower you melt, the shinier the chocolate. Stir constantly as the chips melt until you have a velvet smooth consistency. When the chocolate is melted and smooth, use a spoon to portion it out into the chocolate mold. Then, using the same small spoon to make sure that the chocolate coats the entire mold cup. You want to have a decent 1/4" thick coating of chocolate in the mold.
Place the molds into the fridge or freezer for at least 20 minutes so that the chocolate is able to really harden and become less fragile. When the chocolate is hardened, remove from the freezer and prep the molds to be filled.
To prep the molds, stretch the edges of each cup so that the chocolate pulls away from the silicone. Then turn the mold over onto a towel or parchment paper and gently push on the top of the dome so that the chocolate bombs release from the mold. Next, put the bombs back into the mold so you can fill them. This will make it a lot easier when it's time to take them out of the silicone for good.
Filling the molds is pretty easy. Put about 1 tsp. of hot chocolate powder in the dome followed by your toppings. You should be able to fit in about 5-6 mini marshmallows and some additional toppings. When the domes are filled, use some of the remaining melted chocolate and cover the bottom of the domes. Pop the finished bombs into the freezer for another 20 minutes so that they have time to harden.
Before packaging them up, take a few minutes to decorate them! Melt the chocolate melts according to the package directions, then pull the bombs out of the freezer, pop them out of the molds (they should come out easily), and give them a little decorating. Then package with the instruction to pour 3/4 cup of steaming hot milk over the top, stir, and enjoy!