Rant: froze my butter for 20 minutes before creaming it and my cookies finally stopped spreading
I have been fighting flat cookies for like two years now. Every batch came out thin and greasy, spreading into one big sheet pan puddle by the time the timer went off. I tried chilling the dough overnight, I tried a different brand of flour, I even swapped out my baking soda thinking it was old. Nothing worked. Last week my oven thermometer read 375 when I had it set to 350, so I fixed that first, and that helped a little. Then a lady at the church bake sale in Dayton told me her trick is to cube the butter and freeze it for 20 minutes before creaming it with the sugar. I tried it Tuesday, and those cookies held their shape with a nice thick middle instead of a pancake. The butter was still cold enough to stay a bit chunky but soft enough to cream. Anyone else mess with cold butter like this, or am I late to something everybody already knows?
The part about the butter being "still cold enough to stay a bit chunky" is where I kinda disagree with you, since cold butter traps air pockets while you cream it and that air is what makes cookies puff in the oven. If your dough was still spreading after you chilled it overnight, that points more to your butter being too soft at the start or your flour measuring being off, not the butter temp at creaming time. Freezing it for 20 minutes is really just a workaround for a warm kitchen, so fix the kitchen temp and you won't have to babysit your butter in the freezer.