Whisk flour, cocoa powder, baking soda, and salt in a medium bowl until no cocoa lumps remain. Set aside.

Beat butter, granulated sugar, and brown sugar on medium-high speed until light and fluffy, about 3 minutes. Scrape the bowl halfway through.

Beat in eggs one at a time, then vanilla, until fully incorporated. The mixture should look glossy and smooth.

Reduce speed to low and gradually add flour mixture. Mix just until no dry streaks remain. Do not overmix.

Fold in chopped chocolate with a spatula, distributing evenly throughout the dough. The dough will be thick and sticky.

Scoop 2-tablespoon mounds of dough onto parchment-lined baking sheets, spacing 2 inches apart. Chill in the refrigerator for 15 minutes while you preheat the oven to 350F.

Bake until tops are cracked and edges are set but centers still look slightly underdone, 10 to 12 minutes. Rotate pans halfway through baking.

Let cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely. They will firm up as they cool.