Using microwave-safe container (not glass), melt about 2/3 of the chocolate in the microwave. When chocolate start to melt, stir with spatula accasionally untill the chocoalte about 90% melted.
Add the remaining chocolate, a little at a time, allowing it to melt completely before adding more chocolate. Stir with spatula untill all chocolate is melted and not hot to the touch.
You can also melt chocolate using double boiler method, where steam from the water melt chocolate. For this method you need to add chocolate in a large heatproof bowl (not glass) and place the bowl over the pot with water. Make sure the bowl is large enough to sit on the rim of the pot and not touch the water. Then the process is the same, when chocolate almost melted you need to add more chocolate and stir with spatula.
When you have chocolate ready, you can continue with the next step. Fill each of the cavities of the silicon mold with chocolate about halfway.
Using spoon spread the chocolate to the top of each cavity.
Using both hands, pick up the mold and tilt the mold back over the bowl of melted chocolate to shake out any excess.
Place mold in the fridge to set for 10-15 minutes. Repeat with other molds.
Remove the molds from the fridge and carefully unmold half spheres.
Heat a large pan untill it gets warm, not too hot. After that slightly melt the rim of a chocolate spheres in the warm pan. Do not melt all spheres, just a half of them.
Place melted spheres open side up and fill them with hot cocoa mix and mini marshmallows.
Melt the rim of remaining half and seal the Hot Cocoa Bombs with another warmed half sphere.
Using a spoon, drizzle some of the chocolate back and forth over the bombs to decorate and top with sprinkles or marshmallow.
Let the bombs to set at room temperature for 20-30 minutes or untill completely set.