Its name derives from the Dutch word koekje which means little cake, and arrived in the English language through the Dutch in North America. It spread from American English to British English where biscuit is still the more general term.
Cookies can be baked until crisp or just long enough that they remain soft, depending on the type of cookie. Some cookies are not cooked at all. Cookies are made in a wide variety of styles, using an array of ingredients including sugars, spices, chocolate, butter, peanut butter, nuts or dried fruits. The softness of the cookie may depend on how long it is baked.
A general theory of cookies may be formulated this way. Despite their descent from cakes and other sweetened breads, the cookie in almost all its forms has abandoned water as a medium for cohesion. Water in cakes serves to make the base (in the case of cakes called 'batter') as thin as possible, which allows the bubbles – responsible for a cake's fluffiness – to form better. In the cookie, the agent of cohesion has become some variation of the theme of oil. Oils, be they in the form of butter, egg yolks, vegetable oils or lard are much more viscous than water and evaporate freely at a much higher temperature than water. Thus a cake made with butter or eggs instead of water is far denser after removal from the oven.
Oils in baked cakes do not behave as water in the finished product. Rather than evaporating and thickening the mixture, they remain, saturating the bubbles of escaped gasses from what little water there might have been in the eggs, if added, and the carbon dioxide released by heating the baking powder. This saturation produces the most texturally attractive feature of the cookie, and indeed all fried foods: crispness saturated with a moisture (namely oil) that does not sink into it.
Classification of cookies
Cookies are broadly classified according to how they are formed, including at least these categories:
Commercially-produced cookies include many varieties of sandwich cookies filled with marshmallow, jam, or icing, as well as cookies covered with chocolate which may more closely resemble a type of confectionery.
Biscuits (cookies) in the United Kingdom
A basic biscuit (cookie) recipe includes flour, shortening (often lard), baking powder or soda, milk (buttermilk or sweet milk) and sugar. Common savoury variations involve substituting sugar with an ingredient such as cheese or other dairy products. Note that this is not the only type of cookie in England. In the UK the term cookie often just refers to chocolate chip cookies or a variation (e.g. oats, smarties).