In a small saucepan, bring water to a boil. Whisk in cocoa until mostly smooth with some lumps. Reduce heat to medium and whisk in milk until cocoa powder is dissolved. Bring to a simmer and whisk in chocolate, sugar, and salt.
Reduce heat to low and whisk until chocolate is smooth and incorporated. Taste and add more sugar if desired (I like 2 additional tablespoons for ¼ cup total). Remove from heat and stir in vanilla. Transfer to a slow cooker or clean coffee urn for serving.
To substitute store-bought mix, cook according to package instructions and transfer to a slow cooker or clean coffee urn for serving.
To substitute single-serve packets or pods, set them out next to an electric tea-kettle or pod coffee maker.
To assemble the hot cocoa bar:
Place the hot cocoa on one side of the table next to a selection of mugs. Turn the slow cooker (if using) to "keep warm" and set a ladle nearby. If using an urn, set a dish under the spout to collect any drips.
Adjacent to the hot cocoa, arrange the toppings in bottles or bowls with spoons and tongs for serving. Start with the whipped cream and sauces, the toppings, the garnishes, and finally the stirrers. Consider labeling the items so everyone knows what is what.
On the far side of the table, include a stack of napkins and baskets or jars full of spoons. Decorate the table with wintery greenery or ribbons in the colors of the season.
Hot cocoa: It's easy to make delicious Hot Chocolate from scratch and serve it from a coffee urn or slow cooker, but it's okay to substitute store-bought hot cocoa mix, packets, or pods.
Milk: Hot chocolate tastes more decadent and delicious with whole milk, but it’s still plenty rich and chocolatey if you use 2% milk.
Bittersweet chocolate: Do not substitute semi-sweet chocolate; it will leave an artificial after-taste.
Sugar: Start with 2 tablespoons sugar and add more to taste (I add a full ¼ cup when I make this recipe).
Yield: This Hot Chocolate recipe makes 4 cups (32 ounces or 1 quart).
Storage: Store leftovers covered in the refrigerator for up to 4 days. Some separation may occur, so stir to recombine while reheating.