Make the ganache. Heat the heavy cream and add in any of your flavorings. Add in your chocolate and stir to combine until the chocolate is smooth. Set aside to cool and harden.
Add the chocolate to a double boiler and stir until the chocolate is melted.
Evenly divide the 12 silicone molds, then turn the molds upside down to let the excess drip for a few seconds. Turn right side up and scrape the excess from the surrounding areas of the mold. Chill to harden, then repeat the process two more times. Make sure the edges have enough chocolate in particular.
Chill the chocolate to harden fully, then carefully peel away the chocolate from the mold.
Met the edges of the chocolate shells and quickly add the ganache and marshmallows, then seal. Rub away any excess melted chocolate and let it harden close.
Add a single bomb into your mug and top with steaming hot milk and stir.
Don't work the chocolate too hard as it can snap easily. Do not press the shells together too tightly when sealing. Use any extracts or other flavors in your ganashe for extra flavor.