Use an electric mixer to cream together the butter, granulated sugar, brown sugar and salt until light and fluffy, about 3 minutes.
Add the egg and vanilla, then beat until just incorporated, about 1-2 minutes more.
Slowly add the flour, baking soda and baking powder and mix until just combined.
Stir in the chopped chocolate chunks and pecans until evenly distributed. Be careful not to over-mix.
Preheat the oven to 375 degrees. Scoop out heaping tablespoons of dough and place them on a baking sheet lined with parchment paper about 2 inches apart.
Press them down slightly with your fingers, then top each one with a little sprinkle of flaky sea salt.
Bake for approximately 9-12 minutes, or until they're just golden on the outside but the middles still look doughy. Less baking time will result in chewier cookies, while more baking time will result in crispier cookies.
Allow them to cool for a few minutes on the pan, then use a spatula to transfer to a wire rack. Serve while they're still warm.