Preheat oven to 350℉. Line a baking sheet with parchment paper.
Begin by browning the butter. Place the butter in a small sauce pot and bring up to a simmer on medium heat. Cook for about 8-10 minutes stirring often or until little brown bits form on the bottom of the pan and it smells nutty. The butter will foam up twice and after the 2nd time the milk solids will start to brown. Keep a close eye on it and stir constantly as it will brown quickly at this stage.
Set aside and let cool slightly for about 10 minutes.
In a medium bowl combine the flour, baking soda, baking powder, sea salt and cinnamon together. Whisk together.
In a stand mixer fitted with a paddle attachment add both sugars and the cooled brown butter. Mix together on medium for 2-3 minutes. It will look like it’s separating but it’ll come together once you add the eggs. Add in the eggs one at a time and the vanilla, mixing thoroughly between egg additions. Mix on medium for 1-2 minutes or until combined and creamy.
Next with the mixer on low, slowly add in the flour mixture and mix until you no longer see any flour bits, about 1 minute. Add in the oats and mix for 30 seconds. Stir in the chocolate chips by hand.
Let dough rest for 10 minutes.
Using a 1 1/2 tbsp. ice cream or portion scoop, scoop the batter onto the lined baking sheet leaving a 2-inch border around the cookies because they spread. Sprinkle with flaked sea salt.
Bake for 9-10 minutes. Let cool slightly on the sheet tray before removing to a cooling rack and letting cool fully. Continue with remaining dough. Makes 46 cookies.