So my cookies were always ending up flat as pancakes, no matter what recipe I used. It was driving me nuts, especially when I wanted to impress friends. After some digging online and a bit of trial and error, I found that chilling the dough for at least an hour is key. The butter firms up, so they don't melt too fast in the oven. I also started using a scoop to keep them uniform, which helps with even baking. Now they come out thick and chewy, just how I like 'em. Seriously, such a simple fix that made a huge difference. Give it a shot if you're having similar troubles!
My last batch spread like crazy until I cut the white sugar in half and used all brown sugar. A thicker, darker baking sheet made a big difference too, it stopped the bottoms from burning before the centers set.