01 - Preheat oven to 350°F and line two baking sheets with parchment paper.
02 - Whisk together flour, baking soda, salt, cinnamon, and nutmeg in a medium bowl.
03 - Using an electric mixer or whisk in a large bowl, beat butter, brown sugar, and granulated sugar until light and creamy, about 2 to 3 minutes.
04 - Add eggs one at a time, mixing well after each addition. Blend in vanilla extract.
05 - Gradually add the dry ingredients to the wet mixture, stirring just until incorporated.
06 - Stir in oats thoroughly, then fold in raisins or chocolate chips and nuts if preferred.
07 - Drop rounded tablespoons of dough onto the prepared baking sheets, spacing about 2 inches apart.
08 - Bake for 10 to 12 minutes, or until edges are golden and centers are set.
09 - Let cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool fully.