Use the back of a small spatula to spread the chocolate all around the silicone cups, focus on the upper edges as the chocolate will slide down a little bit as it hardens.
Set the silicone tray on the metal baking sheet and set it into the freezer for about 10 minutes.
Spread a second layer of chocolate into the cups, again, focusing on the edges. The chocolate does not need to be really thick, just as even as possible.
Return to the freezer on the tray for another 5 minutes.
Heat a plate or pan that you can use to melt the edges of the cups.
Melt 3 of the 6 edges.
Fill add about ½ a tablespoon of cocoa and some marshmallows. Repeat for all three.
Melt the edges of the other 3 cups, one at a time. Then one at a time set them onto the filled cups. You may need to rotate the cups a bit to find the closest connection. Repeat with the other two bombs.
Store the bombs at room temperature.
To Make Hot Chocolate
Heat your milk to about 140 degrees.
Set a hot chocolate bomb into your mug.
Pour the hot milk over the top and watch the magic happen.
Stir for about 30 seconds to fully incorporate the melting chocolate and cocoa powder.
Be careful not to over fill them or it will be harder to put the two halves together