Melt the chocolate in a double boiler or in the microwave in 30-second increments, stirring after each, until melted and smooth. Stir in the tahini, vanilla and salt. It will thicken as it cools. (At this point, it can be kept in a jar in the fridge for about 1 week. Great spread on toast or by the spoonful!)
Heat the milk in a saucepan, stirring frequently, until steaming. Add the chocolate-tahini mixture and whisk until smooth. Serve hot!