You should flatten your cookies before baking the cookies if you want to create a flat surface for decorating although you shouldn't flatten the cookies before baking if you don't want to create a flat surface.
Flattening the cookies before baking can thin out the cookie dough and make the cookies crispy.
The cookie dough is soft enough that it will spread on it's own.
You also put egg in cookie dough as the eggs in cookie dough works as a leavening agent and also adds color, structure and flavor to the cookies.
The egg added to cookie dough also helps the cookies to spread out and puff up and keep the cookies together while they bake.
Egg yolks also acts as an emulsifier which helps to bind the water and fat together in the dough and the egg yolk fat contributes to the texture and flavor of the cookies.
Adding too many eggs is the most common reason for cookie dough to turn out like cake batter.
Adding not enough eggs can result in dry and crumbly cookies.
When adding eggs to cookie dough you should mix each egg in the dough separately and thoroughly.
Melting butter in cookie dough when baking cookies helps improve the flavor and tenderness and helps contribute to the structure and rise of cookies.
Melted butter also helps cookies achieve a fudgy texture and creaming butter and sugar together helps to incorporate air into the cookie dough which helps the cookies rise.
Brown sugar in cookies helps the cookies retain moisture and keep the cookies moist and prevents too many air pockets forming.
Brown sugar when added to cookies helps to prevent too many air pockets from forming and helps to trap moisture in the cookies which makes the cookies more moist as the brown sugar helps retain moisture in the cookies.
When you use only brown sugar in a cookie recipe, the cookies will have more moisture and typically be chewier.
Since the molasses in brown sugar also is acidic, it reacts with baking soda to help leavening; it will be puffier.
Baking soda does not make cookies crispy but instead the use of baking soda in your cookies makes the cookies soft and fluffy.
When added to dough, baking soda releases a carbon dioxide gas which helps leaven the dough, creating a soft, fluffy cookie.
Baking soda is generally used in recipes that contain an acidic ingredient such as vinegar, sour cream or citrus.
The use of brown sugar in your cookie recipe is what makes cookies soft, moist and chewy and white sugar and corn syrup is what makes your cookies crispy.
When your cookies turn out flat and crispy it's because you didn't use enough flour.
Not using enough flour in your cookie dough can make your cookies turn out flat and crispy.
Sometimes cookies turn out flat and crispy or flat and crunchy because your oven is too hot too.
If your cookies repeatedly turn out flat, no matter the recipe, chances are your oven is too hot.
Here's what's happening.
The butter melts super quickly in a too-hot oven before the other ingredients have firmed up into a cookie structure.
Therefore, as the butter spreads so does the whole liquidy cookie.
When you're making cookies you can mix butter and shortening in your cookies.
Mixing both butter and shortening in a cookie recipe, you will get the wonderful flavor of butter, while the shortening will keep the cookies from spreading too flat.
The best shortening for cookies is Crisco All Vegetable Shortening.
Cookies that are made with butter spread more and are flatter and crisper if baked long enough.
However, they are more flavorful than cookies made with shortening.
Cookies made with shortening bake up taller and are more tender, but aren't as flavorful.
Egg Yolk acts as a binder in the cookie dough.
Adding egg yolks to the cookies yields a super tender, chewy cookie.
The moisture content of the cookie is what gives cookies a chewy texture.
Any cookie recipes that contain a lot of butter, brown sugar or egg yolks are going to yield soft and chewy cookies, because those ingredients add moisture and retain it for a longer amount of time.
For Chewy Cookies you want to use brown sugar instead of white sugar as brown sugar keeps more moisture in cookies.