How do I fix cookies that spread too much?

Chill your dough in the fridge for at least 30 minutes before baking - this is the easiest fix and works almost every time. You might also check that your butter isn't too soft when you're creaming it, since that can make cookies spread like crazy. If you're using older baking soda or baking powder, they could be losing potency and not setting the dough properly, so swap them out if they've been sitting around forever. I've made countless batches with my kids over the years and temperature control really is the game changer.