Cookies:

1. Pour the oats into a food processor and pulse until the texture is mixed with fine crumbs and whole oats for the best texture in the cookies.
2. Whisk the ground oats with flour, baking powder, cinnamon, nutmeg, baking soda, and salt in a medium bowl.
3. In a separate large bowl, use an electric mixer to cream the sugars and butter together until fluffy. Mix in the eggs and vanilla extract. Gradually add the dry ingredients until everything is combined and the batter is thick, tacky, and sticky. Chill the dough for 30-45 minutes.
4. Preheat the oven to 350°F. Line 3 cookie or baking sheets with parchment paper. Set aside.
5. Use a medium cookie scoop to scoop out 1 ½ tablespoons of cookie dough and drop them on the cookie sheets about 2 inches apart (12 cookies per sheet),
6. Bake the cookies, 1 sheet at a time, for 14-16 minutes or until they are brown around the edges and puffed up in the middle. Let the cookies cool to room temperature.

Icing:

1. Stir the powdered sugar, vanilla extract, and milk together in a small bowl until the icing is smooth and thick.
2. Lightly dip the tops of the cookies in the icing and let them rest on a cooling rack until the icing sets, about 30 minutes. Store in an airtight container on the counter for up to 3 days.