Don't skip the step of chilling the dough both times. When you mix the cookies, the butter becomes softened, which is what causes cookies to spread in the oven. By chilling the dough for 20 minutes before rolling, it makes it easier to roll the cookies into the correct shape. Then, you'll chill the rolled dough a second time, so the butter can harden again and keep their shape in the oven. You can even do this step in advance and keep the rolled dough in the refrigerator until you are ready to bake.