A cookie becomes crispy due to a combination of ingredients, baking techniques, and chemistry:

• Butter and Fat Type : Using butter, especially melted butter, helps cookies spread out more during baking because butter melts at a lower temperature than shortening. This spreading creates thinner, crispier cookies with browned edges

. Substituting oil for butter can also increase spread and crispiness

• Sugar Type : Using more white granulated sugar instead of brown sugar leads to a crisper cookie. Brown sugar contains more moisture and acidity, which makes cookies softer and chewier. Granulated sugar absorbs moisture better, promoting crispness

• Eggs : Eggs add moisture and structure, which tend to make cookies softer. Omitting or reducing eggs results in flatter, thinner, and crisper cookies

• Flour : All-purpose flour with higher protein content contributes to a sturdier structure and better browning through the Maillard reaction, which enhances crispness. Using less flour can also help cookies spread and crisp more

• Baking Temperature and Time : Baking at a lower temperature for a longer time allows cookies to spread fully before setting, resulting in even crispiness. Baking longer until edges brown but not burn also produces a crisp texture

• Dough Handling : Not chilling the dough before baking encourages more spreading and crispiness. Storing cookies in a cookie jar or glass container rather than plastic helps maintain crispness after baking

In summary, crispy cookies are typically made with butter and white sugar, little or no eggs, all-purpose flour, baked at a lower temperature for longer, and baked from unchilled dough to promote spreading and drying out, which yields a thin, crunchy texture