Heat 3 cups milk, 2 tablespoons light brown sugar, 1 teaspoon vanilla and a pinch of salt in a medium saucepan over medium heat, whisking, until the milk is steaming and the sugar dissolves. Gradually add 4 ounces each chopped semisweet and bittersweet chocolate, whisking until melted. Cook, whisking occasionally, until smooth. (Note: This is an extra-thick European-style hot chocolate.) Serve with mini marshmallows, peppermint sticks, whipped cream, mini chocolate chips, toasted coconut or other toppings.