Melt the chocolate candy melts in a small bowl placed over a pot of simmering water. If you are using chocolate chips, you will want to temper the chocolate to make sure it's shiny and pretty. Candy melts don't need to be tempered.
To temper, you will need a candy thermometer. Melt two thirds of the chocolate to roughly 105 F. Then, add the remaining chocolate a little at a time, stirring to melt. Let the chocolate cool to 82 F. Once the chocolate has cooled to 82 F, put it back over the hot water and reheat to 88 - 91 F. Maintain the chocolate at this temperature.
Use a clean paint brush to brush the silicone molds with chocolate. Freeze 10 minutes to set.
Use gloves for this step to avoid fingerprints on your hot chocolate bombs. Heat up a frying pan on medium heat and gently melt the edges of one chocolate bomb half. Pop the chocolate bomb half into a cupcake paper or round cookie holder to hold it while you fill it. Fill with 1 tbsp hot chocolate mix and some mini marshmallows.
Melt the edges of the second half, then put the two halves together. The melted edges will seal.
Let the hot chocolate bombs rest for a few minutes. Melt the white chocolate or colored candy melts. Place the white or colored chocolate in a piping bag and pipe swirls over the hot chocolate bombs. Add some sprinkles!