Preheat oven to 350°F. Line half sheet pan with parchment paper or a silicone liner. set aside.
Add unsalted butter, granulated sugar, and light brown sugar to a large bowl. Beat at high speed until creamy, for about one minute.
Add egg, vanilla extract, salt, baking powder, and baking soda. Beat at medium speed until well combined, about one minute.
Add flour. Beat on low just until combined.
Add oats. Beat on low just until combined.
Using a 2-tablespoon cookie scoop, portion the dough into 8 pieces. Roll the dough between the palms of your hands into smooth, round balls, flatten to about ½ inch, and place 2 ½ inches apart on the prepared baking sheet. (See Tip 4)
Bake at 350°F for 14 to 16 minutes, or until a deep golden brown all over.
Remove the cookies from the oven and let them sit on the baking sheet for five minutes. Transfer them to a wire rack to cool completely. Repeat with the remaining cookie dough.
Yield: 20 4-inch cookies. (See Tip 5)