Evaporation is what gives crinkle cookies their distinct cracked surface: the cookie dough dries out first, before the leavening agents react, forming cracks. To make crinkle cookies, scoops of cookie dough are coated in sugar before baking. That sugar absorbs moisture on the surface of the cookie, drying it out. This promotes the cracking process that gives these cookies their signature look. Some bakers will actually coat the cookie dough in granulated sugar before coating in powdered sugar to promote drying and to form deeper, more prominent cracks.