Cut the butter into small pieces and place them into a small pot over medium heat. Make sure you use a light colored pot so you can easily see when the butter starts to brown.
Stir the butter so it all melts. As the butter is completely melted, it will start to foam and you'll smell a little nuttiness. (Is that a real word?) The color will start to change from yellow to a golden color. Once the butter is golden brown or tan as I like to call it, remove the pot from the heat and transfer the butter to another bowl to cool. Once the butter is just cooled, you can strain out the little sediments in the butter and you'll be left with a brown nutty butter.
In a large mixer, combine the melted browned butter and brown sugar with a paddle attachment. Let whisk for 2 minutes. Add the eggs one at a time, followed by the vanilla extract. Add the flour, baking soda, sea salt and baking powder and slowly combine, making sure not to over-mix the batter. Add the oats and chocolate chips and combine. Refrigerate batter for at least 1 hour. It's very important to chill the dough since we started with melted butter.
Pre-heat oven to 350 degrees. Line 2 baking sheets with parchment paper and set aside.
Using a 1 inch scoop, scoop 12 cookies onto each parchment lined baking sheet and sprinkle the top of each cookie with some flaky salt. Transfer sheets into over and bake for 10-12 minutes until the cookies just slightly turn a golden brown color on the edges but are still soft and chewy in the middle. Remove from oven, transfer to cooling rack. Repeat process for remaining dough.