Whisk together flour, baking soda, and salt. Set aside.
Beat butter and sugars on medium-high until pale and fluffy (approx. 3mins). Reduce speed to medium, add egg and vanilla. Beat until combined.
Reduce speed to low and add flour mixture. Mix until just combined. Fold in dark chocolate chunks.
Refrigerate dough for at least 1 hour.
Preheat oven to 350°F. Line two baking sheets with parchment paper or silicone mats.
Using a large (3 Tbsp) cookie scoop to drop cookies onto your baking sheet spacing at least 3" apart (approx. 6 cookies per sheet). Press down on each slightly to flatten.
Bake for 12-14 mins or until golden on the edges, but still soft in the center.
Let cool on pans for 5 minutes, then transfer onto wire racks to cool completely. Sprinkle with additional sea salt if desired.