Move a rack to the center of the oven and preheat to 325 degrees. Line a baking sheet with parchment paper then set aside.
Cream butter and both sugars together until light and fluffy. Add the eggs one at a time, completely incorporating each egg before adding the next. Beat until everything is completely incorporated, scraping the sides of the bowl often.
Sift the flour, salt, baking soda, baking powder and cinnamon over the wet ingredients and mix just until combined. Add the rolled oats then mix until completely incorporated.
Place rounded tablespoons of dough on the baking sheet. Bake 10−12 minutes or until just set (or just slightly underdone) in the center.
Remove from the oven, allow cookies to rest on the baking sheet 2 minutes then transfer them to a wire rack to cool completely.
One Last Thing
Like raisins or dried fruit such as cranberries or cherries in your cookies? Go right ahead and add them in. About ¾ cup is perfect.