Preheat the oven to 350 degrees F. Line baking sheets with parchment paper.
In a large bowl with a handheld electric mixer or in a stand mixer fitted with the paddle attachment, add the butter, brown sugar, granulated sugar, baking soda, baking powder, and salt. Mix well until light and fluffy, 1-2 minutes, scraping down the sides of the bowl as needed.
Add the eggs and vanilla. Mix until well-combined, scraping down the sides of the bowl as needed.
Measure the oats into a blender or food processor and process until the oats are blended into a coarse powder.
Add the oats and flour to the bowl and mix until a few dry streaks remain. Add the chocolate chips and mix until evenly combined.
Scoop the cookie onto the prepared baking sheets (I use a #40 cookie scoop - it holds a couple tablespoons of dough), spacing them a few inches apart. See note for making/baking large bakery-style cookies.
Bake for 10-12 minutes until just lightly golden around the edges but not too dark. Remove to a cooling rack and let cool completely.
Really Big Cookies: this recipe can also make 9-10 REALLY large bakery-style cookies. I weigh the dough (about 150 g/5.25 oz each cookie) and place them 4- to 5-inches apart on the baking sheet and bake for 13-15 minutes. Oats: I haven't tried using quick oats for this recipe, but it will probably work (use the same amount or slightly less).Chocolate Chips: Ok, fine, you can use milk chocolate chips if you have to. :)Yield: If using a #40 cookie scoop (about 2 tablespoons of dough), the batch will yield around 30-36 cookies. The cookies can also be made extra large, bakery style. Weighing out about 5.25 ounces/147 grams of dough for each cookie will yield about 10 huge cookies (add a few minutes to the baking time).