Preheat oven to 350°. In large bowl, cream together butter, brown sugar, egg and vanilla until smooth. In separate bowl, whisk flour, baking soda, cinnamon and salt together. Stir this into butter/sugar mixture. Stir in oats, raisins and walnuts, if using them. At this point you can either refrigerate dough and then scoop it, or scoop cookies onto a sheet and then chill the whole tray before baking them. Cookies should be two inches apart on parchment-lined baking sheet. Bake them for 10 to 12 minutes, taking them out when golden at the edges but still a little undercooked-looking on top. Let them sit on hot baking sheet for five minutes before transferring them to a rack to cool.
The last trick to getting a really thick, chewy cookie is to chill the dough before you bake it. You can scoop it and then chill it, or, if you?re like us, scoop it, freeze them and store them in a freezer bag so you can bake them as you wish. I find they?re always thicker when baked from the cold ? only a couple extra minutes baking is needed.