Add 5 oz of your chocolate to a medium, microwave safe bowl, and microwave for 30 seconds. Remove the bowl from the microwave and stir. (If you have enough molds to make all 12 domes at once then you can melt 10 oz of your chocolate to start, and add up to 2 additional oz as needed below when tempering)
Continue to microwave in 15 second increments, stirring fully between each, and scraping the sides of the bowl with a rubber spatula, until almost completely melted.
Continue to stir so that the heat of the melted chocolate continues to melt the unmelted chocolate pieces. Check the temperature of the chocolate with an instant read thermometer, to make sure the chocolate reads between 88 to 90 degrees Fahrenheit (for semi sweet chocolate). If the temperature goes over 90 degrees, stir in an additional ounce of chopped chocolate until that is melted, and brings the temperature back down below 90 degrees.
Spoon about 1 Tablespoon of melted chocolate into each of the molds. Use the back of a small spoon to spread it around, making sure to get all the way to the top of the rim, and not leave any exposed areas in the mold.
Place the mold on a small baking sheet and refrigerate for 5 minutes.
Remove the molds from the refrigerator and spoon another spoonful into each of the molds, one at a time. (Don't add chocolate to each of the molds at once because of their cold temperature it will harden too quickly). Use the back of the spoon to spread a second layer of chocolate around each mold, making sure to build up the edges around the rim. (You want the edges thicker so they don't crack).
Place the mold on the baking sheet into the freezer for 10 minutes.
Remove the pan from the freezer and carefully remove the domes from the molds. (Use food safe gloves to keep them fingerprint free).
Repeat the steps if you just have 1 one mold of 6 (You need 12 half domes total).
Once all the shells have been made, microwave a small flat plate for 2 minutes. Place 6 of the domes on the plate, one at a time. Spin them around with a gloved hand to smooth the edges of the mold down. Then place them rounded side down in a cupcake pan, or cupcake liner. Wipe the plate clean.
Fill the 6 domes with the hot cocoa mix, and then mini marshmallows.
Reheat the plate for another 2 minutes in the microwave. Then repeat placing the 6 domes onto the plate, one at a time, onto the hot plate, spinning around as the chocolate melts.
Place them on top of the cocoa filled halves and gently press them together to seal.
Let the hot chocolate bombs set for a few minutes. Then drizzle the top with melted chocolate. Top with sprinkles, if desired.