Preheat oven to 350F and line baking sheets with parchment paper.
In a medium bowl whisk together the 1 1/2 cups all purpose flour, 1/2 tsp baking powder, 1/2 tsp baking soda, 1/2 tsp nutmeg, 1/4 tsp cinnamon, and 1/2 tsp coarse salt. Set aside.
In the bowl of your stand mixer (or a large bowl with electric beaters) cream the softened 1 cup unsalted butter until light and fluffy. Scrape down the sides of the bowl.
Add the 1 cup sugar and 1 cup dark brown sugar to the bowl and continue creaming until light and fluffy, about 3 minutes. Be sure to scrape down the sides of the bowl as needed.
Blend in the 1 Tbsp vanilla extract and then beat in the 2 large eggs, one at a time, taking care to get it all smoothly incorporated. (It helps if the eggs are at room temperature.)
With the mixer or beaters on low add in the flour mixture and mix just until combined.
Add the 3 cups old fashioned rolled oats* and 2 cups raisins and mix until evenly incorporated.
Use a 2 inch ice cream scoop to scoop out 2 inch balls of dough and place them 2" apart on the baking sheet. I bake 6 cookies per sheet. Gently flatten each ball just slightly with your fingers.
Bake for 11 minutes, then remove the pan and wrap sharply on the counter or other hard surface.** This deflates the cookies a bit. Return to the oven and bake for another 8 minutes. The cookies should be golden. If yours are still a bit puffed you can give the pan another sharp wrap to deflate them. Note: the baking time is just an approximation, if your cookies are bigger or smaller than mine or your oven is cooler or hotter your baking time will vary.
Let the cookies cool for a few minutes on the pan and then transfer them to a rack. They are amazing warm or at room temperature. They will get crisper around the edges as they cool.
See make ahead and freezing instructions in the post below the recipe.
Notes
*Do not use quick cooking oats, they will not give the right texture.**The pan banging technique is a now-classic cookie trick popularized by baker Sarah Kieffer (The Vanilla Bean Blog). Rapping a hot sheet of par-baked cookies on a hard surface flattens them and creates crisp crinkly edges with soft chewy interiors.