Step 1

Place all of the ingredients except for the toppings into 3-quart slow cooker (or a 5-quart or larger if you are doubling the recipe): milk, half-and-half, chocolate, sugar, cocoa powder, vanilla, espresso powder, and salt.

Step 2

Briskly whisk to dissolve the cocoa powder as much as possible. Keep whisking until none of it floats to the top; this may take 1 to 2 minutes.

Step 3

Cook on low for 2 to 3 hours or on high for 45 minutes to 1 hour (depending upon your slow cooker; it may finish sooner. Once it's hot and the chocolate is melted smoothly, you can serve it as soon as you like; I prefer to do this on low to make sure the chocolate doesn't burn). Whisk every 45 minutes or so to make sure the chocolate isn’t burning on the bottom of the crock pot. At this point, you can keep it on "low" or switch to "keep warm" if you have that setting. Do not keep it on high, as if the chocolate becomes too hot, it can burn or separate.

Step 4

Ladle into serving cups and add your toppings of choice.