Follow these steps with care to ensure your cookies come out perfectly soft and chewy every single time. The magic is in the details, from creaming the butter properly to the crucial chilling step.

1. Prepare Your Pans and Preheat: Adjust your oven racks to the middle position and preheat the oven to 350°F (175°C). Line two large baking sheets with parchment paper or silicone baking mats. This prevents the cookies from sticking and ensures even browning on the bottom.
2. Combine the Dry Ingredients: In a medium-sized bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, ground nutmeg, and salt. Whisking is important as it aerates the flour and distributes the leavening and spices evenly, so you don’t get a pocket of salt or cinnamon in one cookie. Set this bowl aside.
3. Cream the Butter and Sugars: In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl with a hand mixer, beat the softened unsalted butter on medium speed until it is smooth and creamy. Add the packed light brown sugar and granulated sugar. Increase the speed to medium-high and beat for 3-4 minutes, until the mixture is light, pale, and fluffy. Scrape down the sides and bottom of the bowl as needed. This step is critical; you are whipping air into the mixture, which is the foundation for a soft cookie.
4. Incorporate Eggs and Vanilla: With the mixer on low speed, add the room temperature eggs one at a time, beating well after each addition until it’s fully incorporated. Once the eggs are mixed in, add the pure vanilla extract and beat until just combined.
5. Add the Dry Ingredients: Turn the mixer off and add the dry ingredient mixture to the wet ingredients all at once. Turn the mixer on to the lowest possible speed and mix until the flour is almost combined, with a few dry streaks remaining. Be very careful not to overmix here, as that can develop the gluten in the flour and lead to tough, dense cookies.
6. Fold in Oats and Raisins: Remove the bowl from the mixer. Add the old-fashioned rolled oats and the raisins. Using a rubber spatula, gently fold everything together until the oats and raisins are evenly distributed and the last streaks of flour have disappeared. The dough will be thick and sticky.
7. Chill the Dough (The Most Important Step): Cover the bowl with plastic wrap and transfer it to the refrigerator. Chill the dough for at least 60 minutes, or up to 4 hours. Chilling the dough is the secret to thick, chewy cookies that don’t spread too much in the oven. It solidifies the fat in the butter, meaning the cookies will melt more slowly and bake up taller and softer.
8. Scoop and Bake: Once the dough is chilled, use a medium cookie scoop (about 1.5 to 2 tablespoons) to portion out mounds of dough. Place them on the prepared baking sheets, leaving about 2 inches of space between each cookie to allow for spreading.
9. Bake to Perfection: Bake for 12-15 minutes, or until the edges are lightly golden brown and the centers look slightly underbaked. The key to a soft cookie is to pull them from the oven while the center is still soft. They will continue to cook and set up on the hot baking sheet.
10. Cool for Best Texture: Let the cookies cool on the baking sheet for 5-10 minutes. This allows them to firm up enough to be moved. After this initial cooling period, transfer them to a wire rack to cool completely. This two-stage cooling process is essential for achieving that perfect soft center and chewy texture.