Adjust the oven racks to the upper-middle and lower-middle positions. Preheat oven to 350 degrees. Line 2 rimmed baking sheets with parchment paper or silicone mats.
In a medium bowl or on a piece of parchment paper, sift together flour, baking soda, cinnamon, nutmeg, and salt. Set aside.
In a stand mixer fit with the paddle attachment, or with an electric mixer on high speed, cream butter until pale and fluffy. Add the granulated and brown sugars and beat until the mixture is smooth.
Add egg and vanilla and beat on low speed until blended, scraping down the sides of the bowl as necessary.
Add the flour mixture in batches (about ΒΌ cup at a time) and mix on low speed until just blended. Add the oats and chocolate chips and stir until just combined.
Working with 1 heaping tablespoon of dough at a time, scoop dough into 1 1/2-inch balls and drop on prepared baking sheets about 2 inches apart. You should have 24 cookies.
Bake until the cookies are golden brown, about 12 to 15 minutes. Transfer to wire racks and cool completely.
