In a small, microwave-safe bowl, melt 2 cups of chopped chocolate or chocolate chips in 15-second increments, stirring in between (it's important not to overheat the chocolate). You can also use the doubled boiler method which is even better but requires more work.
Take the molds, and spoon about 2 tablespoons of melted chocolate into each half-sphere. And then using a pastry brush or even the back of a spoon, just spread the chocolate around the sphere so that it's well coated. You need to have a good coating so that the chocolate bombs are not fragile.
Chill the half-spheres - Transfer the molds to the freezer for 15 minutes to solidify. Once set, gently and quickly remove from the molds. The heat of your hands can cause the chocolate to melt, so do this quickly.
It is best to decorate half of the half-spheres at this stage. Lay them on a tray or plate face down, and drizzle with melted chocolate and immediately sprinkle with multi-colored mini chocolate chips or any decoration you're using (before the drizzle hardens).
Return to the freeze for 5-10 minutes to make sure that the drizzle is hardened.
Take the plain half-spheres, and fill each with 1 tablespoon of hot cocoa mix, top with one piece of cosmic brownie if using, and a few mini marshmallows.
And finally to seal, warm up a small microwave-safe plate in the microwave just for 30-45 seconds. And lay each decorated empty half-sphere on the plate for a couple of seconds until it starts to melt and create a "glue", then connect it with the corresponding filled half sphere. Repeat with the remaining.