There’s nothing sadder than flat cookies.  Here are some things you can do to prevent the spread. Use fresh baking soda. While fresh baking soda is key for that crackle cookie top, it’s also imperative to the structure of the cookie. If it’s expired, the dough will spread. Chill the dough. Don’t forget to let the dough chill in the fridge for 2-3 hours. It needs to be completely cold before you bake it. Otherwise, you’ll end up with flat, sad cookies. Use cool baking sheets. It’s a good idea to have two baking sheets so you can let the first one cool while the second one is in the oven. You can also let a baking sheet cool down for a couple minutes and then rinse it under cool water if you don’t have two.  If the cookies spread a little bit too much, when you pull them out of the oven you can use a butter knife or two spoons to gently push them back in towards the center. Be sure to do this while they’re still hot!