Brown the butter: Add the butter to a light-colored saucepan over medium heat.
Stir as it melts, foams, and then turns golden with brown bits on the bottom. When it smells nutty and the milk solids are amber, remove from heat. Transfer to a heatproof bowl and let cool to a warm, pourable state.
Prep your oven and pans: Heat the oven to 350°F (175°C).
Line two baking sheets with parchment paper.
Whisk dry ingredients: In a medium bowl, whisk flour, baking soda, baking powder, salt, and cinnamon if using. Set aside.
Mix sugars and butter: In a large bowl, whisk the brown sugar and granulated sugar with the cooled brown butter until glossy and combined.
Add eggs and vanilla: Whisk in eggs one at a time, then mix in vanilla. The mixture should look smooth and slightly thick.
Combine wet and dry: Switch to a spatula.
Stir the dry ingredients into the wet until just combined. Don’t overmix.
Fold in the texture: Add oats, coconut, chocolate, and pecans. Fold until evenly distributed.
If the dough feels very soft, chill for 15–20 minutes to firm it up.
Scoop the dough: Use a 2-tablespoon scoop (about golf-ball sized) and place dough balls a few inches apart on the prepared sheets.
Bake: Bake 10–12 minutes, until the edges are set and lightly golden and centers look slightly underbaked. They’ll set as they cool.
Finish and cool: If you like, sprinkle with flaky sea salt right out of the oven. Let the cookies rest on the sheet for 5 minutes, then transfer to a rack to cool.