In a Dutch oven over medium heat, combine whole milk, whipping cream, sugar and cocoa powder. Whisk constantly until cocoa powder is combined and sugar is melted.
6 cups whole milk, 2 cups heavy whipping cream, 1/2 cup sugar, 1/3 cup cocoa powder
Add chocolate chips and the vanilla extract and stir until melted.
1 cup milk chocolate chips, 1 1/2 teaspoons pure vanilla extract
Heat thoroughly, then reduce heat to low to keep warm. Don't ever let the mixture come to a boil. Stir occasionally so it doesn't burn.
Serve in warmed mugs with whipped cream, marshmallows and other hot chocolate toppings.