Preheat oven to 350°F and line a baking sheet with parchment paper.

In a large bowl, whisk together the softened butter, brown sugar, and granulated sugar until smooth and fully combined. If the butter is not softened, microwave the stick in its wrapper for about 5 seconds per side until soft but not melted.

Whisk in the egg and vanilla extract until the mixture is glossy and cohesive.

Add the flour, baking soda, and kosher salt. Stir gently just until no dry streaks remain. Avoid overmixing to keep the cookies tender.

Fold in the chocolate chips until evenly distributed throughout the dough.

Using a 2-tablespoon scoop or measuring spoon, portion 12 dough balls onto the prepared baking sheet, spacing them about 2 inches apart. Do not flatten the tops.

Bake for 10 to 12 minutes, until the edges are lightly golden and the centers still appear slightly soft. The cookies may look slightly puffy when removed from the oven.

Immediately sprinkle with flaky sea salt. Let the cookies cool on the baking sheet for 5 minutes, they will continue to set and gently deflate. Transfer to a wire rack to cool completely.