Preheat your oven to 375 degrees F. and prepare a cookie sheet by lining with parchment paper and set aside.
In the bowl of a stand mixer equipped with a paddle attachment, cream the butter and both sugars until light and fluffy.
Add the egg and vanilla and mix until just combined.
Add in the flour, baking soda, salt, cinnamon, and nutmeg and mix until there are no dry spots remaining.
Add your oats to a food processor and pulse 8-10 times until you have a nice coarse crumb. Add those in last and mix until the oats are evenly distributed throughout the dough.
Use a cookie scoop to scoop out 18 balls of dough and place on the parchment lined cookie sheet. (NOTE: I used a 1 ½ Tbsp scoop, but you can use what you have on hand. Just note the servings may be different with different size scoops)
Gently press down the top of each cookie using your hand or the bottom of the cookie scoop.
Bake for 10-12 minutes or until the edges are set and the tops of the cookies are golden brown.
Remove from the oven and allow the cookies to cool for 5 minutes on the baking sheet then transfer to a wire rack to cool completely.
Once the cookies are cooled completely prepare the icing by adding the powdered sugar, milk, corn syrup, and vanilla into a small bowl and whisk until smooth. Add more milk if necessary, about ¼ teaspoon at a time. The right consistency will be when you lift the whisk and drizzle the icing into the bowl, it should disappear back into the rest of the icing after a few seconds.
Once the icing is ready, take one cookie by the bottom and dip the top of each cookie into the frosting and straight back up. Let the extra frosting drip off, then place the cookie dipped side up back onto a wire rack. Continue with each cookie. (NOTE: Do not try to dip them before they are completely cool, the cookie will fall apart when you try to take it out of the icing)
Let the cookies set for 1-2 hours to allow the icing to completely harden.