[header] How to make chewy chocolate chip cookies [title] Preheat the oven to 350ºf/180ºc. [title] Add the vanilla, sugar, brown sugar, eggs, and butter to a bowl. [substeps] Use coarser sugar for thicker, chewier cookies. When sugar dissolves, it acts as a tenderizer that interferes with dough structure. 
This increases spreading because finer sugar dissolves more easily than coarser sugar. So if you want your cookies to remain thick and chewy, use coarse sugar (or use fine sugar for the opposite effect).