Preheat your oven to 350°F (175°C). Line two large baking sheets with parchment paper. This recipe makes a good number of cookies, so you'll likely need to bake in batches.

In a medium mixing bowl, whisk together the all-purpose flour, baking soda, salt, ground cinnamon, and ground nutmeg until well combined. Stir in the old-fashioned rolled oats and set aside.

In a large mixing bowl, using an electric mixer, cream together the softened unsalted butter, packed light brown sugar, and granulated sugar on medium speed until light and fluffy, about 2-3 minutes. Scrape down the sides of the bowl as needed.

Beat in the large eggs one at a time, mixing well after each addition. Stir in the pure vanilla extract until just combined.

Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix the dough. Once the flour streaks are almost gone, fold in the raisins with a rubber spatula until evenly distributed.

Drop rounded tablespoons of dough (or use a small cookie scoop) onto the prepared baking sheets, spacing them about 2 inches apart.

Bake for 10-12 minutes, or until the edges are golden brown and the centers are set but still look soft. The exact baking time may vary depending on your oven and cookie size. For a chewier cookie, slightly underbake them.

Remove the baking sheets from the oven and let the cookies cool on the sheets for 5 minutes before transferring them to a wire rack to cool completely.

Repeat with the remaining cookie dough, ensuring your baking sheets are cool before adding new dough.