It has nothing to do with box or Bosco, but here goes anyway -

When I see the word 'bosky' I think of the phrase 'bosky dell,' which I enountered in poetry somewhere. 'Bosky' means woodsy or shrubby, and a dell is a small, retired valley.

Googling 'bosky dell' produces lots of hits. There are towns, streets, farms and businesses named Bosky Dell. Who'd a thunk it?

Further back in time, 'bosky' is connected to an old French word, 'bocage,' which means woods or shrubbery.

Apparently the only way to link it with the chocolate drink is to stir the Bosco into your milk with a twig.