Begin each batch with a cool cookie sheet to prevent the cookies from spreading too much.
In a conventional oven, it’s best to bake one sheet at a time; Place the cookie sheet on a rack in the center of the oven, leaving space on all sides for air circulation. If you must do two at once, swap shelves and rotate trays halfway through the baking time.
In a convection oven, which uses a fan to circulate air, you can bake several sheets at once. Convection baking will reduce baking time by several minutes; watch the cookies closely until you are sure how long to bake them.
Consider how altitude may change baking temperature and/or time.
