Most traditional chocolate chip cookie recipes start with the same basic ingredients and technique: butter and sugar (a mix of white and brown) are creamed together with a touch of vanilla until fluffy, eggs are beaten in one at a time, followed by flour, salt, and some sort of chemical leavening (baking soda, baking powder, or a bit of both). The mixture is combined just until it comes together, then spooned onto a baking sheet and baked.
When you bake a cookie, here’s what’s going on, step-by-step.
The dough spreads:. As the butter warms, it slackens. The cookie dough begins to turn more liquid and gradually spreads out.
The edges set: As the cookie spreads, the edges thin out. This, coupled with the fact that they are fully exposed to the heat of the oven and are constantly reaching hotter areas of the baking pan, causes them to begin to set long before the center of the cookie does.
The cookie rises: As the butter melts and the cookie’s structure loosens, this frees up water, which in turn dissolves baking soda. This baking soda is then able to react with the acidic components of brown sugar, creating gases that cause the cookies to rise up and develop a more open interior structure.
Egg proteins and starches set: Once they get hot enough, egg proteins and hydrated starches will begin to set in structure, finalizing the shape and size of the finished cookie.
Sugar caramelizes: At its hottest areas—the edges and the underbelly in direct contact with the baking dish—sugar granules melt together, turning liquidy before starting to caramelize and brown, producing rich, sweet flavors.
The Maillard reaction occurs: Proteins in the flour and the eggs brown along with the sugar in a process called the Maillard reaction—the same reaction responsible for giving your hamburger or bread a brown crust. It produces nutty, savory, toasted flavors.
The cookie cools. Once it comes out of the oven, the process isn’t over yet. Remember that liquefied sugar? Well as the cookie cools, that liquid sugar hardens up, which can give the cookie an extra-crisp, toffee-like texture around the edges. Meanwhile, the air inside cools, which causes the cookie to deflate slightly, though when fully baked, the structure lent by eggs and flour will help it retain some of its rise.
It’s a simple technique that hides more complicated processes underneath. So how do you decipher what’s going on? My first course of action was to test out these basic ingredients one at a time in order to determine how they affect the final outcome.