Preheat your oven to 350°F (175°C). Line a couple of baking sheets with parchment paper and set them aside.
In a large mixing bowl (a stand mixer works great for this), beat the cubed butter with both the brown sugar and granulated sugar. Mix until the texture is creamy and everything’s well blended this usually takes about 45 seconds to a minute.
Add the vanilla extract, then beat in the eggs one at a time, mixing well after each addition.
In a separate bowl, whisk together the flour, cornstarch, baking soda, and salt. Gradually add this dry mixture to the wet ingredients, mixing until just combined. Don’t over mix.
Using a spatula, gently fold in the chocolate chips, chocolate chunks, and chopped pecans.
Scoop the dough using a 2-inch cookie scoop or spoon, and place mounds of dough on your prepared baking sheets. Leave about 2 inches between each cookie to allow for spreading. If you like, press a few extra chocolate chunks or chips on top for a prettier finish.
Bake for 8 to 10 minutes or until the edges are lightly golden and set. The centers might still look a little soft that’s perfect. They’ll firm up as they cool.
Let the cookies sit on the baking sheet for 5 minutes after baking, then transfer them to a wire rack to cool completely. If you want, sprinkle a pinch of flaky sea salt on top while they’re still warm.