Start by adding the cocoa powder to a pot, pour in the hot water and whisk until mixed.
Add the cocoa mixture along with the chocolate chips, milk, evaporated milk, and salt to a 6-quart slow cooker or larger.
Cook the hot chocolate on the high setting for 4 hours or on low for 6 hours. Low for 6 hours is what I prefer. Make sure to stir the hot chocolate every hour to keep the chocolate from settling to the bottom.
Keep on the warm setting if you’re serving it hot chocolate bar style with toppings on the side. Leftover hot chocolate can be refrigerated for up to one week and can be warmed in the microwave before serving.