Molecules of chocolate

The Journal of Chemical Education paper on chocolate based demonstrations discusses three key classes of molecules.
Triglyceride is a major component of cocoa butter. It is hydrophobic.

Serotonin is a major component of cocoa powder. It is is largely hydrophilic and so will dissolve in water.

Lecithin is an emulsifier [just like egg which leads to formation of a stable emulsion of oil and vinegar in a salad], an amphiphilic molecule, which promotes mixing of cocoa solids and cocoa butter.