Line up your hot cocoa bomb molds on a sheet tray for easy transferring. My molds have 6 half domes per sheet and I use 2 of them. The 12 domes make 6 hot cocoa bombs. These bombs are 2.7 inches wide. Pour the bag of chocolate chips into a medium sauce pan over low heat. Stir with a rubber scraper until the chocolate is fully melted and smooth.
Use a brush to smooth the melted chocolate all over the inside of the molds. I like to start at the bottom and pull the chocolate all the way up to the top of the mold. Make sure the layer is not super thin, watching for holes or transparent spaces, and also getting the chocolate all the way to the top of the mold. This will be the inside of the bomb - it DOES NOT have to look pretty! It's going to melt anyway! I fill up all 12 half dome molds with 1 bag of chocolate with some left for drizzling at the end.
The chocolate needs to fully harden at this point. You can leave the chocolate on the counter to harden, or speed the process up to about 10-15 minutes in the fridge.
While the chocolate sets, you can get your cocoa mix ready. Put the coconut sugar, cocoa powder, and sea salt in a coffee grinder or small blender and blend to combine and break up the sugar smaller so it dissolves quickly in the cocoa.
Once the chocolate in the mold sets, gently pop them out of the molds onto a tray. Put 4-5 mini marshmallows into 6 of the half dome chocolates. Add 2 teaspoons of the cocoa mix over the top of the marshmallows. If you plan to use sprinkles, you can add those at this time too.
Now you need to put the other half of the chocolate dome on top. Use a warm non-stick skillet to melt the rim of one of the empty domes - this melty chocolate on the rim will "glue" to one of the bottom domes with the cocoa mix/marshmallows to create the full bomb. Let the bombs set for a few minutes so the chocolate sets and the bomb stays together.
You can use the leftover melty chocolate chips to drizzle the tops of the bombs. You could decorate the tops with naturally dyed sprinkles or naturally dyed sanding sugar too. To make the hot cocoa, each bomb will need 1 cup of liquid. Whole milk or milk alternative works. I like to use 1/2 cup water and 1/2 cup coconut milk since coconut milk can be thick. Bring the liquid to a simmer - the hotter the liquid the more "explosive" the hot cocoa bomb will be! You can either set the hot cocoa bomb in the mug and pour the hot liquid over, or you can pour the liquid in, and set the hot cocoa bomb into the liquid. Use a spoon to gently stir the cocoa mix fully, and enjoy!