Aside to Micca, and totally off the subject-sorry, folksMicca, that's almost exactly how we made cocoa when I was a child, living with my grandparents. Oh, we didn't use the rum, of course, and instead of condensed milk we used evaporated, but otherwise it's the same. Most all US-ers just put cocoa in the cup and add boiling water. The cocoa we get here is sweetened, and has dry milk in it.
I think my family did things in a British or Irish way, without even knowing that they were. Thanks for sharing that with us.
Mary McCaffrey