In a saucepan over medium heat, add 3 ½ cups of milk and the chocolate and cook stirring occasionally.
In a bowl, put the rest of the milk and add the cornstarch and stir until it completely dissolved. Reserve.
Once the chocolate has dissolved, reduce the heat to medium-low,add the mixture of milk and cornstarch, and continue cooking stirring constantly, for 7-8 minutes until the chocolate has the desired thickness.
Add the vanilla and salt and stir.