Mix the dry ingredients: In a medium bowl, whisk the flour, ground cinnamon, ground nutmeg, baking soda, and salt. Set aside.
Mix wet ingredients: Using a mixer (with the paddle attachment) or an electric handheld mixer on medium-high speed, cream the softened butter with brown sugar and granulated sugar until light and fluffy, about 2 to 3 minutes, scraping the sides of the bowl as needed. Then, reduce to medium speed and beat in the eggs, one at a time. Next, mix in the vanilla extract.
Combine the dry and wet ingredients: Gradually mix in the dry ingredients mixture into the wet ingredients mixture, until combined and no pockets of flour remain. Do not overmix.
Then, mix in the oats and raisins on low speed (or using a rubber spatula) until evenly incorporated. The dough should be very sticky.
Cover with plastic wrap, making sure the plastic wrap is touching the dough. Refrigerate for 30 minutes. Note: If refrigerating for several hours, let it sit on the counter for 30-40 minutes before using.
Meanwhile, preheat oven to 350 degrees F. Line two large sheet pans with parchment paper.
After the dough has refrigerated for about 30 minutes, use a medium cookie scoop (1.5 tablespoon capacity) to scoop out the dough onto the prepared sheet pans, about 2 to 3 inches apart. Note: If you refrigerated the dough for several hours, lightly press down the cookie dough balls to flatten a little bit. This will help them spread better.
Bake for 11-13 minutes, or until they are slightly golden brown around the edges. Bake in multiple batches. Let cool for a few minutes on the sheet pan and then transfer to a cooling rack to cool completely. Enjoy! Tip to make perfectly round cookies: While they are hot, run a round cookie cutter around each cookie in a swirling motion to reshape the edges. I use a round cookie cutter that’s slightly bigger than the cookie.