Mix all dry ingredients together, including cocoa powder, sugar, and a pinch of salt.

Boil the water in a heavy saucepan.

Dissolve the dry ingredients in the boiling water by whisking over medium heat for about two minutes, keeping it to a simmer.

Add the milk and heat it until it's hot, whisking continually, being careful not to boil.

Remove the mixture from the heat.

Add the cream or half-n-half and the vanilla.

Divide the hot cocoa between four mugs.

Add more cream to cool if needed, or simply wait.