In the medium bowl, whisk together the flour, baking powder, salt, and nutmeg. Set aside.
In the bowl of the stand mixer, mix together the butter and sugars on medium speed until it is light and fluffy, about 5 minutes.
Add the eggs one at a time, mixing for about 30 seconds each time.
Slowly add the flour mixture while mixing on low, just until the ingredients are combined.
Stir in the oats and the raisins gently, just until combined. Make sure that the oats are evenly distributed throughout the dough, otherwise you'll have clumps of oats that don't hold together when baked.
Scoop a ball of dough and roll it in your hands, then drop on the baking sheet, spacing about 2 inches apart. Continue with the remaining dough. Dampen your fingers with water and lightly press down on the top of each dough ball, flattening it slightly.
Bake in the preheated oven for 22 to 25 minutes. The cookies should be golden, but the center should be soft and puffy. Allow the cookies to sit on the baking sheet for 10 minutes, then remove to a wire rack and cool.