With health food stores stocking--and selling--""natural"" mixes, this might be an idea whose time has come. The Shandlers, who have previously revealed to us How to Make All the ""Meat"" You Eat from Wheat, and who contribute here a few health-food howlers of their own (a broth of dried herbs, nutritional yeast, and carrot juice), now suggest that as commercial mixes contain too much sugar and other additives, you can prepare your own mixes to keep on hand for rushed last-minute cooking: Of course when your parmesan comes pre-grated, your garlic powdered, and your parsley, onions, and chilies dried, your own concoction won't taste much different from commercial mixes. And you might begin to wonder how much time you are saving by tossing together arbitrary combinations of dried beans, powdered spices, or whatever. For an Indian raita, for example, you have to grate cucumber and mix it with yogurt just before serving in any case. Our favorite Indian cookbook would have you finish this off simply with cumin seeds freshly dry-roasted and ground, an operation that takes about two minutes and imparts a heavenly aroma to the raita. The Shandlers, though, in keeping with their scheme, call instead for their ""Basic Curried Dressing Mix,"" prepared as much as two months earlier by mixing ten pre-ground spices. Then there is their whole-wheat bread mix: up to two months ahead of time you can spend a few minutes combining flour, powdered milk, instant yeast, and salt, so that all you have to do when you feel like some homemade bread is stir in the wet ingredients, knead, let rise, bake, cool, and eat some four hours later. But then you probably couldn't fill a cookbook with mixes that made sense.