Preheat oven to 350 degrees. Use parchment paper or a silpat mat to line a baking sheet.
Cream the butter, brown sugar and sugar in a stand mixer until light and fluffy (about 2-3 minutes). Scrape the sides of the bowl to make sure all ingredients are blended.
Add in the egg, and vanilla and beat until combined.
Add in flour, rolled oats, baking soda, cinnamon, salt and nutmeg. Stir until all combined.
Scoop out about 1 TBSP of dough for mini cookies (or 1/4 cup dough for large cookies). Place dough balls on prepared pan (12 cookies to a pan if mini cookies).
Bake for about 10 minutes. Remove from oven. Let cool on tray for 10 minutes. Transfer cookies to cooling rack. NOTE: If you decide to make the BIG cookies, you’ll need to bake them for 12-13 minutes. Let cookies completely cool down.
ICING INSTRUCTIONS
In a small bowl, whisk the powdered sugar, 1 TBSP milk and vanilla together until smooth. If the mixture is too thick to dip the tops of the cookies in, thin it out with 1 tsp of milk at a time.
Carefully dip the tops of the oatmeal cookies in the sugar glaze and set them back on the cooling rack to set. When the icing sets, enjoy!