Start by browning the butter. You'll take one cup of butter and melt in a medium saucepan, and then continue to cook past the point of boiling. You will do this over medium heat, past the point of the butter foaming, until it turns a nice golden brown, and has a nutty smell. Make sure you are stirring and watching it, because it will turn from perfectly brown to burnt fairly quickly. Once finished browning, pour into a glass bowl and put back in the fridge to solidify again. You will want it to become a soft solid again to start the cookie dough. This should take a few hours.
Preheat oven to 350 F. Line two baking sheets with parchment paper.
Place butter and sugars in the bowl of a stand mixer, fitted with a paddle attachment. Beat on medium-high speed until light and fluffy, 3 to 4 minutes.
Add eggs one at a time, mix until smooth on low speed, anout 30 seconds each egg. Beat in the vanilla.
In a separate bowl, whisk together flour, baking powder, baking soda, salt, cinnamon and nutmeg. Add flour mixture to bowl and mix on low, being careful not to overmix. I usually like to stop mixing when I still have flour remnants around the bowl. Fold in oats and raisins.
Scoop the dough into large balls. I like to use a ¼ cup cookie scoop.
Place 6 cookie balls on your baking sheet. Bake the cookies for 11-14 minutes. You're looking for a nice golden brown outside rim.
Sprinkle with a little flaked salt if you like that kind of thing. You know I do.
Allow cookies to cool on the pan before moving to a cooling rack to hold their shape.