In a large mixing bowl, cream together the butter, granulated sugar, and dark brown sugar until light and fluffy (about 2-3 minutes). Beat in the egg and vanilla extract until well combined.

In a separate bowl, whisk together the all-purpose flour, baking soda, baking powder, and kosher salt. Gradually add to the wet ingredients, mixing until just combined.

Fold in the chopped dark chocolate and pecans. Ensure they are evenly distributed throughout the dough.

Cover the bowl with plastic wrap and refrigerate the dough for 20-30 minutes. Preheat your oven to 350°F (175°C).

Scoop tablespoon-sized portions of dough onto a lined baking sheet, spacing them 2 inches apart. Sprinkle with flaky sea salt if desired. Bake for 10-12 minutes until the edges are golden.

Allow cookies to cool for 5 minutes on the baking sheet before transferring to a wire rack to cool completely.