When those cookies you mixed so carefully become a dismal failure in the oven, staying soft and gooey or even getting puffy, it's disappointing. In most cases, you can fix the problem with a little more cooking time or by adding some extra ingredients before you bake them. With cookies designed to be soft, though, there's not much you can do but grab a glass of milk to wash them down.
More Oven Time
Underdone cookies tend to be gooey, so put them back in the oven for a few more minutes to harden them. Place the baking sheet in the oven at the temperature required by the recipe. Watch the cookies carefully so they don't get too brown; in most cases, two or three minutes is long enough. In the future, bake cookies at a low temperature for a longer time for hard cookies.
It's the Equipment
The type of baking sheet you use can influence the texture of your cookies. Insulated baking sheets tend to produce soft, unevenly baked cookies, while thin aluminum pans bake cookies more evenly, leaving them crisper. Allow cookies to cool completely and dry slightly on a baking rack.
Change the Ingredients
You can try adding more flour to unbaked dough. Flour provides structure in baked goods and can make cookies firmer and crisper. In the future, try adding slightly less fat or replacing some of the white sugar with brown sugar. Brown sugar and fat give cookies flavor and also help keep them soft. By altering these ingredients, you'll end up with harder cookies. Reduce fat by no more than 1/4 to 1/2 cup. High-protein egg whites act as a building block in baked goods, adding structure and a chewy texture.
Try a Different Recipe
Cookies that contain fruit puree or chocolate chip cookies high in butter and brown sugar should be soft. If you prefer crisp, crunchy cookies, stick with recipes intended for that texture, such as ginger snaps or snicker doodles. These cookies don't have a lot of butter or soft ingredients, so they stay crisp. In the case of rolled cookies, rolling them thinly yields a crisp cookie. If you roll the dough more thickly, you'll have softer cookies.