To pulse or chop the oats: place rolled oats in a blender or food processor fitted with a metal blade and pulse 3–5 times, until the oats are about one third the original size. Oats may also be chopped by hand on a cutting board.
Preheat oven to 375°F and line two baking sheets with parchment paper.
In a medium bowl, combine flour, cinnamon, baking soda and salt; set aside.
In a large mixing bowl, beat butter, brown sugar and granulated sugar until smooth and creamy, 3–5 minutes. Add eggs and vanilla extract and mix until smooth. Add flour mixture and blend briefly, followed by the oats and raisins or chocolate chips. Mix just until oats and raisins or chocolate chips are evenly distributed.
Portion dough onto prepared baking sheets, about 2 tablespoons per cookie, leaving about 2 inches between each cookie. Bake until the edges have browned and the center is set, 9–12 minutes. Let cool on the baking sheet for 10 minutes before removing to a wire rack to cool completely. Store in an airtight container.
