O Livro de Pantagruel is the Bible of Portuguese cooking. It is a staple of Portuguese households. My husband bought me a copy last Christmas, and it is incredible. There are hundreds of pages of recipes, descriptions of every spice imaginable and their uses, images to help you understand different cuts of meat, and more. You can order it online from most Portuguese bookshops (Bertrand, Almedina, Porto Editora, Lidel).
I have also followed some recipes by Temperos e Sabores on YouTube. Most of the videos are in Portuguese, but she always includes the written recipe in the video description. She has a lot of traditional Portuguese dishes, and all of the recipes I have used so far have been very good.