In a 4 quart slow cooker, mix the cocoa and hot water together and stir until smooth. This helps prevent the cocoa from becoming lumpy.
Add the sugar, salt, vanilla and milk (optional malted milk powder) and stir to combine.
Heat on high for one hour and then turn down to low or warm while serving.
Notes
To make on the stove top, just pour all the ingredients into a pot on the stovetop and stir until heated through. Stir often as it can burn on the bottom. Try not to let it come to a boil.Keep leftover hot chocolate in a covered container in the refrigerator for 3-4 days.