Place the butter in a medium saucepan and melt over medium heat, stirring often, until it foams, smells nutty, and browns. This will take about 5 to 7minutes. Scrape the browned butter into a medium bowl. Cover and place in the fridge until the butter sets up. It should be soft but not solid. This should take about 45 minutes.
Preheat the oven to 350 degrees F. Line a large baking sheet with parchment paper or a Silpat baking mat. Set aside.
In a medium bowl, whisk together the flour, baking soda, sea salt, and cinnamon. Set aside.
In the bowl of a stand mixer or with a hand mixer, beat the brown butter and sugars together until smooth, scraping down the sides of the bowl with a spatula as necessary.
Add the eggs and vanilla extract. Mix until combined.
Add the dry ingredients and mix on low until just combined. Don’t over mix. Stir in the oats, chocolate chips, and chocolate chunks.
Roll the cookie dough into balls, about 2 tablespoons of dough per cookie. Place the dough balls on the prepared baking sheet, about 2-inches apart.
Bake for 10 to 12 minutes or until cookies are golden brown around the edges but still a little soft in the center.
Remove from the oven and immediately sprinkle with flaky sea salt. Let the cookies cool on the baking sheet for 5 minutes. When they are set up, transfer to a cooling rack to cool completely