Cookbook suggestions for an impatient cook

'An Everlasting Meal" by Tamar Adler isn't exactly a cookbook, but more like a philosophy/methodology of cooking, much of which I think would work well for an impatient cook. I mean, she claims to have served plain bean broth to a guest who came for a meal - you don't get fewer ingredients than that!

Alice Waters The Art of Simple Food has very few ingredients and produces lovely results...

Great ideas, everyone. Thanks so much!

Ditto Nigella Lawson. But as you mention, Mark Bittman is an obvious choice for simple, dependable recipes, e.g., How to Cook Everything and How to Cook Everything Fast. Alice Waters' Art of Simple Food is also full of recipes that depend on not lengthy but great quality ingredients, and straightforward technique.

I would recommend Nigella Lawson's How to Be a Domestic Goddess. She's not into fiddle-y (her word) foods with long lists of ingredients. The format is more novel form than cookbook, but the recipes are mostly very good and easy. This was her first and it's my favorite.

I'd give her The Fat Duck cookbook, and a massive grin.

Consider Rozanne Gold, chef at the Rainbow Room, author of 12 cookbooks, award-winner etc who made a thing of 3 ingredient recipes (e.g., cooking, baking, healthy, for kids,).
The thing is, from 3 ingredients she often gets very impressive and complex-tasting results.
See her listings at Amazon in case one or more strikes you as good for your sister.
http://www.amazon.com/Rozanne-Gold/e/B000APODVM/ref=dp_byline_cont_book_1
Cooking 1-2-3

Have you seen Nigel Slater's EAT? Ingredient lists are so short, they don't exist!