Step 1

Add the oats to a blender or food processor, and blend until the oats process into an oat flour, about 30 seconds. It's okay to have a few chunks left in the oats -- they do not need to be ground into a super-fine flour.

Step 2

In a large bowl, beat together the butter, granulated sugar, and brown sugar until light and fluffy (about 3 minutes). You can use a stand mixer with the paddle attachment, if you'd like.

Step 3

Add the eggs and vanilla, and beat to combine.

Step 4

Add the ground oat flour, all-purpose flour, baking powder, baking soda, salt, cinnamon, and nutmeg. Stir to combine well.

Step 5

Let the dough rest for 10 minutes (this gives the oats time to absorb some of the liquid in the recipe).

Step 6

Preheat the oven to 350 degrees F., and line a baking sheet with parchment paper or a baking mat.

Step 7

Scoop a generous tablespoon of dough into your hands, and roll it in to a ball (this will help your cookies to be very round when baked).

Step 8

Place on the cookie sheet 2 inches apart, and repeat with remaining dough.

Step 9

Bake for 11 to 13 minutes, or until the edges are light brown (if you like a crisper cookie, bake them a bit longer until the whole cookie is a light brown).

Step 10

Remove from the oven, and let the cookies cool on a wire rack.

Step 11

To make the icing, stir together the powdered sugar and milk to form a thin icing.

Step 12

Hold onto the cookie, and dip just the top into the icing. Let the icing drip off, and then return the cookie to the cooling rack, icing side up. Repeat with remaining cookies.

Step 13

Enjoy right away, and store extras in an airtight container in a single layer (the icing can make them stick together if you stack them).