Sabrina Veksler posted:
My cookie recipe calls for 60g of cornstarch to 490 g flour, and they don't spread. I'm a believer.
Cornstarch typically has a "lightening" effect on the cookie crumb (makes the crumb a bit more delicate). It's the ratio of total starch to other liquid/fat ingredients that usually dictates how much a cookie spreads. You likely have a high ratio of starch to other stuff in your recipe.