Prep: Preheat oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone baking mats.
Mix wet ingredients: In a large bowl, whisk together melted butter, white sugar, and brown sugar until smooth. Add eggs one at a time, whisking well after each. Stir in vanilla extract.
Add dry ingredients: Sift cocoa powder, flour, baking soda, and salt into the wet mixture. Stir with a spatula or wooden spoon until just combined and no dry streaks remain.
Fold in chocolate chips: Gently fold in chocolate chips until evenly distributed throughout the dough.
Chill (optional but recommended): Cover the bowl and refrigerate dough for 30–60 minutes for thicker, chewier cookies with deeper flavor.
Scoop and salt: Using a 1½‑tablespoon cookie scoop or spoon, roll dough into balls and place them 2 inches apart on prepared baking sheets. Sprinkle each cookie lightly with flaky sea salt.
Bake: Bake for 10–12 minutes, until edges are set but centers still look slightly soft. Do not overbake.
Cool: Let cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.