Preheat the oven to 350F then line a baking sheet with parchment paper and set aside.

Cream the butter, brown sugar, and granulated sugar together until combined. Add in the egg and vanilla and mix until light and fluffy.

Mix in the flour, oats, cinnamon, nutmeg, baking soda, and salt, making sure to scrape the sides until the mixture is combined.

Using a large cookie scooper, scoop out 8 equally sized cookie dough balls, place them on the prepared baking sheet, gently press down on the cookies to about 1 inch in thickness, and bake them in the preheated oven for 10 minutes. Make sure to not overbake them so they stay soft and gooey.

Let the cookies cool down on the baking sheet for 20 minutes then move to a cooling rack to cool down fully.

In a medium bowl, whisk the powdered sugar, milk, and vanilla together until combined to make the glaze. You want the mixture to be thick and creamy but thin enough to dip the cookies in. If it's too thick, add 1 tsp milk at a time and mix.

Dip the top of the cooled-down cookies into the vanilla sugar glaze then place them back on the cooling rack. Allow them to set fully before enjoying them!