Place a pot on the stove with a couple inches of water. Place a bowl over the pot and add the chocolate.
Heat over medium low heat and stir until chocolate is melted and smooth.
Remove pot from the stove, leaving the bowl in place. (this will keep the chocolate the proper consistency as you work)
Place the chocolate molds on a baking sheet. Add about 2 teaspoons of chocolate to each cavity of the molds and, using a pastry brush, brush the chocolate to cover the inside making sure to get right to the edges.
Place the tray in the freezer for about 5 mintues to allow the chocolate to set.
Remove the tray from the freezer and repeat the process of filling the molds and brushing the chocolate over the inside (you will be adding another 2 teaspoons of chocolate per mold). Return the pan to the freeze for another 5-10 mintues until fully set.
Remove the chocolate bowl from the pot and place a clean plate on top of the pot to warm.
Carefully stretch the molds with your hands to loosen the chocolate.
Add 1 tablespoon of cocoa mix to 6 of the halves and add 5-6 mini-marshmallows.
Working one at a time, remove the empty halves from the mold. Place an empty shell face down on the warm plate to heat the edge. When you see the edge beginning to melt, remove from the plate and press to a filled half. Hold in place for a few seconds to help seal. Repeat with remaining shells.
Place the tray back in the freezer for a few minutes to make sure the chocolate seal has set. Then remove from the freezer and carefully pop the bombs out of the mold.
Decorate with a drizzle of melted chocolate and sprinkles, or any way you like.