Place all ingredients into the slow cooker and stir to combine.
Cover the slow cooker and heat on Low for 3 hours, whisking every 30 minutes (be sure to get the chocolate off the bottom of the crock), until the chocolate chips are fully melted and well incorporated.
Switch the crockpot to the Warm setting if not serving all at once so it stays hot. Remember to stir it occasionally.
Notes
This recipe can also be heated on the stove top.
High quality chocolate chips give the best flavor.
Use Nonfat evaporated milk for a lighter version (It won't be as creamy).