I would recommend Penelope Casas' "The Food and Wines of Spain". I am not sure if this will fit your idea of "thick", but it is considered by many to be the definitive work on Spanish cooking...it is also a bit old, but being that most of the recipes are classic Spanish fare, I don't think they have changed much since 1982 when it was last revised (I think that is right, that is the edition I have). She has since written several others that cover more specific areas of spanish cooking such as tapas etc. but food and wine is a book that offers a great general educational approach to Spanish cooking.