I know exactly the hot chocolate you are speaking of. I studied in italy this past spring and fell in love with the thick hot choclate. While I was there I asked one of the student (american) barista's how she did it. She steamed some milk with the steam wand of an espresso machine, but not fully up to temperature. Then she mixed in the hot chocolate mix (just a plain old powder) and steamed it some more. Once it was near temperature (the temp for milk for cappuccinos and such is 150-160d F) she slowed the steam down and for some reason that thickened it up. Now, I just tried to replicate that at home and didn't get the same results. However, I'm sure there is some trick I'm not getting. Once milk is past 170-180F is scalded. Perhaps it needs to get to that point? not really sure. Good luck!