Now that the Secrets to Baking Well book is offered in the same LE regions as the Libro de Arte Coquinaria, the latter seems impossible to receive. Over the last several months, I have to have done at least 30-40K LE attempts in this area, and received 12 Baking Well books since Crafting was released, but not one of the Libro. Even before Crafting was released, I tried to get this book at least 10K times to no avail. 

One suggestion that came from our guild is to have some sort of token system where once you collect enough of a certain token, you can trade them for one of these hard to get recipe books. For example, let's say you gain one of these tokens at a 5% drop rate per LE attempt, and it requires 5,000 tokens to purchase a golden book (Libro, Emerald Tablet, Royal Protocol, etc.), 2,500 for a silver level, and 1,000 for a brown level, etc. This way we can EVENTUALLY get these books one way or another, either through a natural drop via LE, or by spending tokens to purchase it.