Place the molds on a flat surface like a cutting board or baking sheet and freeze for at least 15 minutes. I find the spheres are best to handle and assemble once they’ve had time to really chill in the freezer and 15 – 20 minutes is a good amount.
Depending on the thickness of the chocolate shell, you may want to do a second coat, spreading melted chocolate onto the first hardened coat and chilling it again.
Gently peel the silicone mold back and pop the half-spheres out. Place them on a piece of parchment paper. Fill six of the semi-spheres with your hot chocolate mix and marshmallows.