01 - In a large bowl, beat softened butter, brown sugar, and granulated sugar on medium speed with an electric mixer until light and fluffy, about 3–4 minutes. Add eggs one at a time, mixing well after each addition, then blend in vanilla extract.
02 - In a separate bowl, whisk together all-purpose flour, unsweetened cocoa powder, baking soda, and salt until thoroughly combined.
03 - Gradually add dry mixture to creamed butter mixture, mixing on low speed until just combined. Gently fold in semi-sweet chocolate chips and dark chocolate chunks if using. Do not overmix.
04 - Cover the dough and refrigerate for 30 minutes to improve texture and prevent excessive spreading during baking.
05 - Preheat oven to 350°F. Line baking sheets with parchment paper. Portion chilled dough into 24 equal scoops and place them 2 inches apart. Gently press extra chocolate chips onto the tops.
06 - Bake cookies for 9–11 minutes until edges are set and centers are just slightly underbaked. Immediately sprinkle with flaky sea salt. Cool on baking sheets for 5 minutes, then transfer to a wire rack to cool completely.