The best flavor to add to chocolate is vanilla; next to that, cinnamon.
Beyond these two things one should use great caution, as it is very easy
to spoil the fine natural flavor of the bean. Chocolate absorbs odors
readily; therefore it should be kept in a pure, sweet atmosphere. As
about eleven per cent. of the chocolate bean is starch, chocolate and
cocoa are of a much finer flavor if boiled for a few minutes. Long
boiling, however, ruins their flavor and texture.