Whisk the flour, baking soda, salt, cinnamon, and nutmeg together in a bowl; set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter, granulated sugar, and brown sugar together.
Increase speed and add the eggs one at a time, beating well after each addition.
Reduce to low speed and add the flour mixture slowly, mixing until just incorporated.
Add the oats and raisins and mix just to combine. Do not overmix.
Scoop the dough into 70g portions, roll into spheres, and arrange in a single layer on a baking sheet. Freeze for at least 30 minutes, or transfer to a zip-top bag for longer storage.
Preheat the oven to 325°F convection or 350°F conventional.
Arrange frozen dough balls at least 2 inches apart on parchment-lined baking sheets.
Bake for 20 to 23 minutes, until the edges are golden brown and the centers no longer look raw. Start checking at 20 minutes.
Video
Notes
Yield: Approximately 18 cookies at 70g each. Freeze before baking: Baking the dough from frozen is what keeps these cookies thick. Do not skip this step; room-temperature dough will spread before the structure sets. Doneness cue: Pull the cookies when the edges are golden brown and the centers look just set, not wet. They will firm as they cool. Storage: Store in an airtight container at room temperature for up to 10 days, or freeze baked cookies in an airtight container for several months.