I do not own many cookbooks, but I think this one is of the first ones I ever bought. Michel Roux is a culinary legend.
From basic recipes, like how to make your own stock and the 5 mother sauces, to advanced techniques and sauces for literally anything.
The last few pages of the book contain a directory for matching sauces to any type of dish or ingredient.
If you want to start somewhere, this book is an absolute classic.