01 -
Add the whole milk, heavy cream, sweetened condensed milk, chocolate chips, cocoa powder, vanilla, and salt to a 4-quart slow cooker.
02 -
Whisk until the cocoa powder is mostly moistened. The chocolate chips will still be whole at this point.
03 -
Cover and cook on low for 1 1/2-2 hours, whisking after 30 minutes and then every 20-30 minutes, until the chocolate is melted and smooth.
04 -
When the hot chocolate looks glossy and fully combined, switch the slow cooker to warm. Do not let it boil.
05 -
Ladle into mugs and top with marshmallows, whipped cream, chocolate shavings, or crushed peppermint. Stir the pot occasionally as it sits.