In a separate bowl, whisk the flour, baking soda, cinnamon, and salt together. Add to the wet ingredients and mix on low until combined. Beat in the oats, raisins, and walnuts (if using) on low speed. Dough will be thick, yet very sticky. Chill the dough for 30-60 minutes in the refrigerator (do the full hour if you’re afraid of the cookies spreading too much). If chilling for longer (up to 2 days), allow to sit at room temperature for at least 30 minutes before rolling and baking.

Roll balls of dough (about 2 tablespoons of dough per cookie) and place 2 inches apart on the baking sheets. I recommend using a cookie scoop since the dough can be sticky. Bake for 12-14 minutes until lightly browned on the sides. The centers will look very soft and under-baked. Remove from the oven and let cool on baking sheet for 5 minutes before transferring to a wire rack to cool completely. The cookies will continue to “set” on the baking sheet during this time.