If you prefer a less sweet cookie, you can reduce the granulated sugar to 3/4 cup, but you will lose some crispness. Do not over bake these cookies. The edges should be brown, but the rest of the cookie should be light in color.
Adjust the oven racks to upper-middle and lower-middle positions and heat oven to 350 degrees. Line two large baking sheets with parchment paper.
Whisk the flour, salt, baking powder, and nutmeg together in a medium bowl; set aside.
In a standing mixer fitted with the paddle attachment, beat the butter and sugars at medium speed until light and fluffy, about 2 minutes. Add the eggs, one at a time, and mix until combined, about 30 seconds.
Decrease the speed to low and slowly add the dry ingredients until combined, about 30 seconds. Mix in the oats and raisins until just incorporated.
Divide the dough into 18 portions, each a generous 2 tablespoons, and roll them between your hands into balls about 2 inches in diameter. Place the dough balls on the prepared baking sheets, spacing them about 2 inches apart.
Bake, switching and rotating the sheets halfway through the baking time, until the cookies turn golden brown around the edges, 22 to 25 minutes. Cool the cookies on the baking sheets for 2 minutes; using a wide metal spatula, transfer the cookies to a wire rack and cool to room temperature.