Sometimes when making drinking chocolate from actual solid chocolate you'll notice parts that don't fully dissolve.
The parts that don't dissolve is usually the cocoa butter. This is due to the natural cocoa butter scalding when really hot milk or steamed milk is used. We recommend creating a slurry and then adding more milk slowly and mixing constantly. This will generally fix any issue when making drinking chocolate from real chocolate and not cocoa powder.
One way we make organic drinking chocolate here in the office is, we fill a mug full of the organic chocolate medallions. We boil water and then slowly pour into the mug over the medallions. We stir and add very little water at a time. The end result is a dairy free yummy drinking chocolate that is thick and wonderfully organic.
Soy lecithin won't normally have a positive or negative result when making drinking chocolate from actual chocolate with cocoa butter (it is generally cocoa butter that has the influence). Soy lecithin could however have a positive influence with cocoa powder when mixing with liquids.
Our drinking chocolate powder is a cocoa powder non lecithinated cocoa (it requires whisking to mix well). We opted to avoid lecithin for many reasons and we have found our cocoa, because of the quality, mixes easily without any lecithin. Simply mix and whisk and add sugar as desired. It is a personal favorites for pure chocolate flavor.