Assemble your three-piece molds first. Remove the top piece, and the inserts and set them nearby. Have the bottom piece ready to receive the chocolate. Set up a muffin tin with 6 liners. We'll use this later to hold the chocolate shells.
Melt your candy coating according to package instructions. Melt in the microwave in bursts of 20-30 seconds, stirring between each blast. Stop when the majority of chocolate is melted and there are only a few lumps left. Stir until remaining chocolate lumps have melted completely.
Add chocolate to the fill line of your mold. Repeat for each cavity, 6 in total across the two molds.
Place the flexible insert, second piece of the mold into each cavity, pressing down slightly so the chocolate starts to spread (does not need to come all the way up the sides at this point.)
Once a set of three has the flexible insert, use the top third piece of the mold to press into the cavities so the chocolate climbs fully up the sides and stops at the lip of the flexible insert. Repeat for the second mold.
Check the cavities lips for air bubbles or thin chocolate and use your fingers to press out the air pockets or redistribute chocolate as needed.
Refrigerate the molds for approximately 10 minutes. (This length of time worked well for guittard a'peels, your chocolate may vary. It can be left for longer as needed.)
Carefully demold the chocolates, placing them in the muffin tin. If the right consistency, they should come out of the molds with minimal coaxing. If stuck a little, gently squeeze the mold cavities near the edges to loosen it. You can also look for air bubbles--you want to see the chocolate retracting from the plastic. Leave the flexible insert in for now (though it's no problem if it slips free).
Carefully peel away the flexible insert. I find it helps to use a chopstick to minimize fingers touching or melting the spheres. I pull away using one hand and use the tip of the chocolate to hold the inside of the sphere for more leverage to separate the plastic.
Prepare fillings. Add marshmallows, cocoa powder, sprinkles, chocolate, or fruit. Add filling for an individual bomb to a small cup or bowl.
Heat a small frying pan on the stovetop, or heat a flat ceramic plate in a toaster oven. Remove from the heat.
Working quickly, grab one half of the bomb, and press the lip to the plate for a second or two until the edge just melts. Pour in the fillings. Repeat the melting process with the second half and press the two halves together. Set back into the muffin tin. Allow to cool for 15-20 seconds or until set.
Melt any additional chocolate and drizzle over the top. Sprinkle on any toppings like sprinkles or fruit.