I'm not sure—certainly for someone who has a collection of around 5,000 cookbooks—it is really possible to name three essential cookbooks, but these are certainly titles that have influenced, inspired and gratified me, and continue to do so.

The Cook's Companion by Stephanie Alexander
This is a huge book, in ambition, scope and page-length and is an utterly comprehensive, but also lyrical, guide to ingredients and what to do with them. It is not illustrated, but no illustrations are necessary: this is about writing and cooking. I don't believe it is claiming too much to say that every kitchen should have a copy.

The Tassajara Bread Book byEdward Espe Brown
When I first started making bread, I kept a copy of this by my bedside for support and comfort, and another copy provided the same in the kitchen. If you are new to bread-making, this is for you; if you are an old-hand, consider it invaluable, also. It is another volume unapologetically free of photographs, but so full of wisdom.

Classic Home Desserts by Richard Sax
For Europeans, there is something exotic, in a counter-intuitively wholesome way, about culinary Americana in general, and baking in particular. The late, lamented Richard Sax's collection of recipes actually has a wider geographical remit, but most of its charm lies in its serious contemplation of, and practical instructions for, home baking traditions, presented in a style that is both charming and elegant.
Nigella Lawson's Nigellissima publishes in the US this month from Clarkson Potter.
It was published by Chatto & Windus in the UK/ANZ last October.