Why did my cookies spread too much?
Most commonly: butter was too hot, the dough was warm, or the baking sheet was still hot from a previous batch. Let the melted butter cool until it is warm, not hot to the touch, and always start on a cool sheet. If your kitchen is warm or your dough feels loose, chill the dough for 20 to 30 minutes.
How do I make them thicker?
For thicker cookies, chill the dough for 30 to 60 minutes, scoop tall mounds (not flattened), and use slightly larger portions. If you want maximum thickness, you can chill up to 1 hour. You can also shape each scoop like a little cylinder for extra height.
Can I make these without cornstarch?
Yes. Cornstarch helps with tenderness, but the cookies will still be soft. If skipping, avoid overbaking and use the bread storage trick.
What chocolate works best?
I like semi-sweet chips plus chopped chocolate (a bar or chunks). Chips hold shape, chopped chocolate melts into puddles. If you prefer sweeter cookies, use milk chocolate chips for half the chocolate.
Why do the centers look underbaked when I pull them out?
That is the point. The cookies finish baking from residual heat on the tray. If you wait until the centers look fully done in the oven, they will set up dry.
Do pan color and ovens matter here?
Yes. Dark pans brown faster, so start checking 1 to 2 minutes early. And if your oven runs hot, the edges can set before the centers stay gooey. When in doubt, pull them when the edges look set and the middle still looks soft.