Preheat the oven to 350F then line a baking sheet with parchement 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 more to a cooling rack to cool down fully.