Combine milk, chocolate chips, condensed milk, heavy cream, and vanilla extract in a slow cooker set to Low. Cook, stirring occasionally, until heated through, about 2 hours. Let cool until safe to drink, about 5 minutes.
You can add Baileys(R), Godiva(R) liqueur, or mint to this and it really sets off the flavor too.
This can also be made on the stove at any temperature, just so long as it gets to that delicious warm stage.