This is the formula I find most helpful when I'm designing a new or changing and old recipe:
About cookie making
Using the correct ingredients is key. Follow the recipe closely and measure ingredients carefully for best results.
Fats Cookies are made primarily with butter, margarine or shortening. Fats play a major role in the spread of a cookie--whether a cookie keeps its shape or flattens in the oven. Shortening and margarine are stable, and will help cookies keep their original unbaked shapes. Butter melts at a much lower temperature than other solid fats--it melts at body temperature, resulting in a “melt-in-your-mouth” burst of flavor. Cookies made with butter tend to spread out. Butter is essential in certain cookies, such as shortbreads; if they don’t hold their shape, consider lowering the amount of butter, sugar, or baking soda in the recipe. The amount of fat also affects the cookies: in general, more fat equals flat, crispy cookies while less fat equals puffier, cake-like cookies. Whipped spreads are not suitable for baking: use solid sticks of margarine instead.
Flour also affects how cookies behave. Most cookie recipes call for all-purpose or pastry flour. Both bread flour, with its high protein content, and cake flour, which is high in starch, produce cookies that tend to spread less. (The gluten in the bread flour and the absorbant starch in cake flour are responsible for the similar results.) Higher flour-to-liquid ratios are needed in shortbread and crumbly-textured cookies.
Baking Powder and Baking Soda are the two most common leaveners in cookies. Baking soda is simply bicarbonate of soda, while baking powder is a combination of bicarbonate of soda plus cream of tartar, an acidic ingredient. Baking soda neutralizes the acidity of the dough, allowing the cookies to brown in the oven. Since baking powder already contains its own acid, it will not reduce the acidity in the dough, and the resulting cookies will be puffier and lighter in color.
Sugars: Like fats, sugars liquefy in the oven. The type and amount of sugar used play a big role in cookie performance. White sugar makes a crisper cookie than brown sugar or honey. Cookies made from brown sugar will absorb moisture after baking, helping to ensure that they stay chewy. Most chocolate chip cookie recipes contain both brown and white sugars. If you lower the amount of sugar called for in a cookie recipe, the final baked cookie will be puffier than its high-sugar counterpart.