Set up a double boiler to melt your chocolate; put a large pot of water half way full on the stove over medium high heat. Place a heat proof bowl over the pot that fits on the pot without touching the water.: The steam heated bowl produces gentle, even heat, which protects the chocolate from scorching. As the water simmers below, you will notice the chocolate beginning to soften around the edges, releasing a warm, cocoa aroma, and the occasional tiny steam swirl under the bowl. This indirect heat keeps the texture smooth, so you avoid graininess. A common mistake is letting the bowl touch the water or the water boil vigorously, which can overheat the chocolate and cause it to seize.
Chop up your semisweet chocolate and melt it in the double boiler until just melted, stirring occasionally. Remove from heat once nearly all the chocolate has melted and continue to stir it until all the chocolate has melted. Your chocolate should reach about 90℉ do not let it get to 100℉.: When the chocolate is nearly melted it will form glossy ribbons as you stir, and the smell will turn richer with cocoa notes. I stop heating at about 90℉ to preserve the temper structure, then remove the bowl and continue stirring off heat until fully smooth. This resting stirring helps distribute the residual heat, producing a silkier finish. Avoid pushing the temperature to 100℉, because that will break the temper and dull the shine.
Once your chocolate has melted, fill the cavities of your silicone sphere molds only a tablespoon at first, use a pastry brush to coat the cavities, allow the chocolate to cool to room temperature, about 5-10 minutes. Add another tablespoon of melted chocolate to each cavity and use the pastry brush to coat the wall evenly again. Allow the chocolate to harden completely at temperature for at least 20 minutes. If your melted chocolate begins to harden while you’re waiting for the first layer of chocolate to harden you can place it back on the double boiler to melt it again, but don’t let it sit over the heat for too long, keep it there until it has just melted again.: Starting with a thin layer ensures an even shell with no weak spots. Use a pastry brush to coat each cavity, painting the chocolate up the sides while the surface of the bowl still gives off gentle warmth. Let this layer cool to room temperature, about 5 to 10 minutes, until it firms but is not brittle. If the chocolate thickens before you finish, briefly return it to the double boiler until just melted again. Don’t rush the drying step, or you may end up with uneven, fragile shells.
Once your chocolate spheres are cooled and hardened, fill half of them with 1 tablespoon of your hot chocolate mix and 1 heaping tablespoon of mini marshmallows.: The second layer builds strength and helps create a pronounced snap. As you brush, you will see the shell start to look more opaque and the surface grow glossy in a steady way. Allow the shells to harden at room temperature for at least 20 minutes so they set properly. If the room is warm, chilling briefly can help, but avoid shocking the chocolate, which can cause bloom. A typical error is applying a single thin coat only, resulting in shells that crack when handled.
Wearing gloves, release the unfilled chocolate shells from the mold, but let them rest in the cavities. Paint or pipe a border of melted chocolate onto the edges of the unfilled chocolate cavities and place them on the filled shells to assemble. If your melted chocolate hardens while you’re waiting for the shells to cool, you can place it back on the double boiler to melt it again, but don’t let it sit over the heat for too long, keep it there until it has just melted again.: The dry filling should sit neatly in the hollow without compacting too tightly, so the powder disperses freely when the bomb melts. The visual is delightful, little white marshmallows peeking out from the dark shell. Don’t overpack the cavity because it will interfere with sealing the halves together and cause spillage when you try to close them.
Allow the assembled spheres to cool for 15 minutes before removing from the mold. You can carefully trim any excess chocolate from the joining seam.: Gloves keep fingerprints off the shell and maintain a clean finish. Gently ease the shell edges free and let them sit, then paint or pipe a thin border of melted chocolate along the edge of the unfilled shells as glue. Place them carefully onto the filled halves to assemble, pressing lightly to create a seam. If your melted chocolate firms up while you’re working, rewarm it briefly until fluid again. Avoid handling the shells directly with warm hands because the heat will soften the chocolate and mar the surface.
To decorate the outside of the bombs you can pipe or paint them with melted white chocolate, the remaining chocolate you didn’t use in the bombs, and any sprinkles you would like.: Letting the assembled bombs rest ensures the seam sets firmly, preventing leaks when they are later warmed. You will notice the seam lose any sheen as it hardens and the chocolate sound become more solid when tapped. After removal, you can trim excess chocolate with a warm knife for a neat finish. Rushing this stage is a frequent mistake, as removing them too soon can break the seal and spill the filling.
To use the bombs, heat 1 cup of milk per bomb until nearly boiling either in the microwave or on the stove. You can either place the bombs in the bottom of the mug and pour the hot milk over top of it, or fill the cup with milk and place the bomb on top!: Decorating adds personality and seasonal flair, and the contrast of white chocolate against dark shells is visually appealing. Use a piping bag or a small spoon to drizzle, and press sprinkles on while the decoration is still wet so they adhere. Work in a cool environment so the decorations don’t slide off. If your piping chocolate thickens, warm it gently until it flows smoothly again.
To use the bombs, heat 1 cup of milk per bomb until nearly boiling either in the microwave or on the stove: Hot milk liquefies the shell and dissolves the filling into a luscious cup of cocoa. Pour the milk over the bomb in a mug and watch the chocolate bloom, releasing hot chocolate mix and mini marshmallows . Be cautious when heating milk; overheating can scald and create an unpleasant film, so remove it just before it reaches a rolling boil. A common mistake is using too cool milk, which will not fully melt the shell and leave clumps of powder.
You can either place the bombs in the bottom of the mug and pour the hot milk over top of it, or fill the cup with milk and place the bomb on top: Both methods work well and produce the sensory reveal we all love. Pouring permits a dramatic cascade, while placing the bomb on top creates a slower melt that is fun to watch. If you place the bomb on top, stir as it softens to encourage even melting. Don’t leave the bomb sitting in water or on wet surfaces, as moisture can cause the chocolate to bloom or stick.
