My mother-in-law is recently retired, an absolutely terrible cook (she admits this herself) and says that she wants to learn how to cook better now that she has more time on her hands. I'd love to get her a classic cookbook as a gift for her upcoming birthday and wanted some recommendations here. Important to note is that she is not someone with a diverse or 'sophisticated' palate--she refuses to eat sushi and a standard meal in her home is burgers with a side of horrifically overcooked green beans. "Cheese dreams" is another classic meal at their home: a slice of American cheese on a defrosted hamburger bun, topped with bits of bacon (cut up using a kitchen scissors) and then cooked in the oven. So, I don't want anything overly ambitious or fancy, as she wouldn't be interested in this.
Of course I thought of Joy of Cooking, and also How to Cook Everything, but wanted to see if anyone had any other recommendations. Books with explicit instructions on technique and general cooking principles (i.e. if the vegetable loses all trace of color you may have cooked it for too long) would certainly be handy for her.