Preheat the oven to 350 degrees F and line a cookie sheet with a sheet of parchment paper.
In a medium sized bowl, whisk together these dry ingredients: flour, baking powder, salt, and baking soda.
In a large mixing bowl, cream the butter, white sugar and brown sugar until well combined, light and fluffy (about 1 minute). Scrape down the bowl with a spatula.
Next, with the mixer on medium-low speed, add the egg and vanilla extract, mixing until well combined (30-60 seconds). Scrape down the sides of the bowl if needed.
With the mixer on low speed, add the flour mixture and mix just until incorporated (this may take 20-30 seconds). Be careful not to over-mix.
Fold in the oats until well combined.
Scoop the dough into 2 tablespoon mounds and roll them to form balls. Place them about 2.5 inches apart on the lined baking sheet(s) as they will spread.
Bake about 13-16 minutes until golden brown and centers are slightly soft. Using a spatula, move to a cooling rack.
Notes
Using quick oats in this recipe (rather than the old-fashioned) will result in cookies that while still good, are a bit more thick and chewy rather than thin and crisp.
Keyword crisp oatmeal cookies, crispy oatmeal cookies