The perfect chocolate chip cookie

Thick and chewy or thin and crispy? How to get the chocolate chip cookie you really want

Linda Lau Anusasananan, Andrew Baker, Christine Weber Hal

What makes a cookie crisp or crunchy?

Reducing the amount of ingredients that hold moisture--flour, egg, and brown sugar--makes it easy for liquid to evaporate, producing crisp cookies. The fat, which goes up proportionately when other ingredients are cut back, gets hotter than the water in the dough and drives out the moisture. Fat also makes the dough softer and melts when hot, making the cookies spread. For crispness, bake cookies longer at a lower temperature to give them more time to spread before they firm. Then bake long enough to dry and brown them evenly to develop the maximum toasty flavor and crisp texture throughout.

What else makes cookies spread as they bake?

We've had many calls and letters from cooks having trouble with favorite recipes. All of a sudden, their cookies are spreading excessively. Most often the culprit is low-fat butter or margarine spread, which has about 20 percent more water, used in place of regular butter or margarine. It's this extra liquid that's causing the problem. Low-fat products can't be used interchangeably with regular fats for baking without recipe adjustments.

Cookies also spread when you drop high-fat dough onto a hot baking sheet; the heat melts the dough, and cookies spread before they're baked enough to hold their shape.

"When others follow my recipe for chocolate chip cookies, they turn out crunchy. Mine turn out chewy. Why?" asks Bobbie Barrett of San Carlos, California.

The way they measure ingredients and the real temperature of their ovens are the usual reasons cooks get different results from the same recipe. Flour should be stirred to loosen and fluff it, then spooned gently into a dry-measure cup (the kind you fill to the rim), and the top scraped level. If you tap the cup or scoop flour from the bag, the flour gets packed down and you can easily add 2 to 4 extra tablespoons flour per cup.

You can scoop up white sugar; it doesn't pack. But you should firmly pack brown sugar into a dry-measure cup and scrape the top level. Dry ingredients should not be measured in heaped-up cups or spoons; scrape dry ingredients level with the surface of the measuring tool. Measure liquid ingredients with liquid-measuring (usually glass or plastic) cups.

If your cookies bake faster or slower than the recipe indicates they should, chances are your oven thermostat isn't registering accurately. It's a good idea to double-check oven temperature with a thermometer and adjust oven setting as needed.