Chop chocolate into very small slivers.
Put chopped chocolate into small pot over simmering water. Take care not to let pot containing chocolate to touch simmering water.
Stir over heat until mostly melted then remove from heat. Temperature should be 88º-89ºF for milk chocolate and white chocolate or 88º-91ºF for dark chocolate.
Stir to completely melt chocolate then use a spoon to coat the molds with a thin layer of chocolate. Refrigerate to harden.
Add a second thin coat of chocolate to the hardened chocolate. Take care to go all the way to the edge so they do not crumble from being too thin. Refrigerate to harden.
Carefully remove from mold. *If the edges start to break add another thin layer of melted chocolate to the rim and cool to harden.*
Fill half the chocolate cups with ½ tsp-1 teaspoon of cocoa mix and 5 marshmallows.
To close, heat an empty pan on medium low heat. Touch an empty chocolate cup to the heated pan for just a second to melt just the rim of the chocolate. Then, very gently line melted chocolate rim to a filled chocolate cup to create a closed sphere. Allow to cool.
Decorate outside of chocolate bombs if desired.
To serve, heat a cup of very warm milk and drop hot chocolate bomb inside. Allow to dissolve them stir well. Enjoy!