3cupswhole milkmust be whole for the best texture!
1cuphalf-and-halfor heavy cream if you want to make this outrageously decadent
6ouncesdark or bittersweet chocolate*coarsely chopped (between 62% and 70%; the darker, the more intense the chocolate flavor will be; I used 66%)
1tablespoonunsweetened cocoa powder or Dutch process cocoa powder
2teaspoonspure vanilla extract
1teaspooninstant espresso powder or coffee powderoptional for a more intense flavor
Toppings of choice: marshmallowswhipped cream, a drizzle of caramel, a handful of extra chocolate chips
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.
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.
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.
Ladle into serving cups and add your toppings of choice.
*I do not recommend chocolate chips, as they do not melt as smoothly. Since chocolate is the primary ingredient, be sure to use good quality. Lindt and Ghirardelli are both excellent. I also had good luck testing with the Baker's brand bittersweet chocolate bar.
TO STORE: Refrigerate leftovers for up to 4 days.
TO REHEAT: Rewarm cgently in a saucepan on the stovetop over medium-low heat, whisking to combine.