Start by combining the cocoa, sugar and a pinch of salt in a saucepan. Blend in ⅓ cup boiling water and bring the mixture to a light boil while you stir. Simmer and stir constantly for about 2 minutes. Make sure it doesn’t scorch.
Stir 3 ½ cups of milk into the mixture and heat until very hot. Do not let the mixture boil at this point. Remove it from the heat and add vanilla. Divide into four mugs and add cream to the mugs of cocoa. This will cool it to drinking temperature.