i am seeking the most "classic" baking cookbook for a gift - is there an equivalent to Mastering the Art of French Cooking or the Joy of Cooking for baking?
I'd go Baking Illustrated which is from the Cooks Illustrated folks. It has chapters on quick breads, yeast breads, pizza/flatbread, pies/tarts, pastry, crisps/cobblers, cakes, and cookies/brownies. The instructions are very detailed, and there's a good amount of food science. Not a lot of pictures, but good illustrations when needed for explanation.
Bakewise, by Shirley Corriher, is another good one. Great deal of information about what happens and why in the baking realm. And of course, any of Dorie Greenspan's books...
Dorie Greenspan ranks right up there with Julia. I have never, not once, failed with any of her recipes. Or Nick Malgieri's recipes, for that matter. I love them both so much that, yes, I'd marry either one of them. Like Julia, both are gifted teachers who want you, their students, to bake as successfully as they do
Unfortunately, the universe of baking has two planets that circle around each other in the kitchen: Breads and Sweets. Malgieri is one of the few who does both. If you don't think his newest book, "the Modern Baker," fits the bill, take a look at "Baking with Julia," which was written by Dorie Greenspan. You could also pair Greenspan's "Baking: From My Home to Yours," with the lovely "The Bread Baker's Apprentice."
I'm not as hot about Christopher Kimball and Cook's Illustrated as I once was--as with Martha, I've gotten all pumped up about a recipe only to have it turn out just okay, no ooomph. I've let my kids borrow those books and I've yet to ask for them back.
I really admire and love Baking with Julia by Dorrie Greenspan. It isn't classic in the sense of being as old as the ones you mention, but it is a classic in the sense that it is a great learning and foundational tool. The techniques and recipes come from 'America's Best Bakers' and was a PBS television series too, where the Bakers presented to Julia Child. I can't say it is as comprehensive as Mastering the Art or Joy, but the selection is wide and finely chosen. There are simple recipes, there are complex recipes. There is a foundational chapter on basics and types of pastry and dough. There are breads, pastries, cakes. Everything I've made from it has been delicious. Read the Amazon reviews for more insight. The book is large and handsome with beautiful photographs.
I started baking with Maida Heatter's wonderful books about desserts. Her instructions are impeccable and easy to follow--it's like having a master baker looking over your shoulder and telling you what to do.
I agree with nutcakes. Julia Child's big Baking book has been my go-to ref for many years. I use many of its recipes, but also consult it for basic technique (much as I often use her The Way to Cook for basics/not so basics; less exhaustive, but a broader scope of cuisines than Mastering's classic French.) Anyway, JC's Baking makes a lovely gift - beautiful photos and design.
Another almost iconic book (though just for cake,) is Rose Levy Beranbaum's Cake Bible. Broad array of well-tested recipes, with lots of useful explanation of the mechanics/chemistry of baking . She also has a Pie and Pastry Bible and a Bread Bible - I haven't used them, but would assume they're similar in approach.
Baking with Julia is my all-time favorite cookbook. Written by Dorie Greenspan, It's based on the PBS show that Julia hosted.
Second to that would be The Flavor Bible (not specificaly a cookbook, but a great source of inspiration), with BakeWise running a very close third.
"The Breadbaker's Apprentice" by Peter Reinhart became an instant classic. And it's a very handsome books. One of the best reviewed cookbooks of the year was "Tartine" by Elisabeth Pruett and Chad Robertson of San Francisco's Tartine Bakery. I haven't been able to look at it yet but I know it's up for a number of prizes.
For bread, try James Beard's "Beard on Bread" and I also second Maida Heatter - I have "Book of Great Desserts." The recipes from both Beard and Heatter are just impeccable and the results are invariably memorable. You will learn to bake from these masters - and you won't be bored if you're already an ace. These are time-tested and treasured.
Most of the above are fairly recent and very good. But there's an older one---I hope it's still in print--by Marion Cunningham. It's called the Fannie Farmer Baking Book, and in addition to very good recipes it incorporates several foundational recipes, like an angel food cake done step by step---perfect for someone with less baking experience. The covers of mine are just about worn away; I pulled it out most recently for her fabulous mincemeat cookies. (The only way to eat mincemeat in my opinion!) Even if it's out of print, it's worth looking for used. I also think the baking books put out by the King Arthur Flour people are quite good.
King Arthur Flour Baker's Companion has a fantastic balance between basic explanation info at the beginning of each section and really good recipes. I'm not a big baker and I've just started baking breads regularly this past year. Everything has been great.