Do NOT substitute margarine or shortening for the butter. You will have a completely different cookie – a “cakey” cookie instead of a “chewy” cookie. These cookies spread out on the cookie sheet, so don’t crowd them. The cookies are “lacey” and chewy. If you make them too big, they will run together on the cookie sheet. Don’t overbake them or they will be crispy instead of chewy. When in doubt, take them out of the oven and allow to finish “baking” on the cookie sheet outside of the oven. In my experience, in my oven, if I bake 2 or 3 batches at a time (on all the oven racks), the top batch is not done, the bottom batch is burned and the middle batch is a combination of the two. So, I suggest the cookies be baked one batch at a time in the center of your oven. This dough can be made ahead of time and refrigerated or frozen. If you are doing either of these, I suggest that you place the prepared dough on wax paper and roll it into a log, twisting the ends. If you refrigerate this dough, it is very hard, so difficult to scoop from the bowl, so making a “log” is your best bet. Then you can cut the logs into coins to bake. If frozen, defrost in the refrigerator prior to baking. Adjust cooking time to accommodate the fact that the cookie dough is cold. Or cut into coins, place on cookie sheet and wait until they are room temperature to bake.