Prep the oven and pans: Heat oven to 350°F (175°C). Line two baking sheets with parchment paper.
Combine dry ingredients: In a medium bowl, whisk flour, baking soda, and salt.
Set aside.
Mix sugars and butter: In a large bowl, whisk melted butter with brown and granulated sugars until smooth and glossy, about 45 seconds.
Add eggs and vanilla: Whisk in the egg, then the yolk, followed by the vanilla, until the mixture looks thick and creamy.
Fold in dry ingredients: Add the flour mixture and stir with a spatula until just combined. Do not overmix.
Stir in chocolate (and nuts): Fold in chocolate chips or chunks, and nuts if using, until evenly distributed.
Optional chill: Chill dough 20–30 minutes for thicker cookies and deeper flavor. If short on time, you can skip this step.
Portion the dough: Scoop 2-tablespoon mounds (about 35–40 g each) onto lined sheets, spacing 2 inches apart.
Bake: Bake 9–12 minutes until edges are set and centers look slightly underdone.
The tops should be pale golden with soft centers.
Finish and cool: If desired, sprinkle with flaky sea salt right out of the oven. Let cookies cool on the sheet 5 minutes, then transfer to a rack to cool fully.