When hosting a hot chocolate party for a large group, there are a few things you can do to keep the hot chocolate warm throughout the event.
First, make sure to use a large enough pot or slow cooker to accommodate all of the hot chocolate. If possible, heat the milk on the stovetop before adding the chocolate so that it doesn't have to spend as long in the warmer. You can also add a little bit of water to the milk when heating it to help prevent scorching.
Once the hot chocolate is made, keep it in an insulated container or thermos. If using a slow cooker, set it to warm or the lowest setting so that it doesn't continue to cook the chocolate and make it bitter. Stir occasionally to help distribute the heat evenly.
To keep things extra-cozy, provide guests with blankets or lap throws and set up a fire if you have one!