01 - Place whole milk, heavy cream, chocolate chips, and unsweetened cocoa powder into a large slow cooker.
02 - Whisk granulated sugar and a pinch of salt into the slow cooker until thoroughly incorporated.
03 - Cover and heat on low for 2 hours, stirring once halfway through, until chocolate fully melts and mixture is velvety smooth.
04 - Whisk in pure vanilla extract just prior to serving.
05 - Lower heat setting to 'keep warm'. Ladle hot chocolate into mugs and provide optional toppings for customization.