Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the unsalted butter, packed light brown sugar, and granulated sugar. Cream the mixture on medium speed until light and fluffy, about 2-3 minutes.
Add in the egg and vanilla extract. Mix on low speed until well incorporated.
In a separate bowl, whisk together the all-purpose flour, cocoa powder, baking soda, and sea salt. Sift the cocoa powder if it’s lumpy.
Gradually add the dry mixture to the wet ingredients, mixing on low speed until just combined.
Gently fold in the chocolate chips until evenly distributed throughout the dough.
Using a cookie scoop or tablespoon, drop rounded balls of dough onto a prepared baking sheet, leaving about 2 inches of space between each cookie.
Press a few more chocolate chips into the tops of each cookie and sprinkle with flaky sea salt.
Bake in the preheated oven for 10-12 minutes, or until the edges are set but the centers look slightly soft.
Allow the cookies to cool on the baking sheet for about 5 minutes before transferring them to a wire rack to cool completely.