Preheat the oven to 475°F.
Add the flour, cornstarch, baking soda, white sugar, and brown sugar to a medium mixing bowl.
Cut the butter into half-inch chunks and put it into another large mixing bowl. Add the egg and vanilla and mix at medium speed until totally creamy and combined.
Add the dry ingredients in cup-fulls while mixing.
When combined, mix in the chocolate chunks, chips, and chopped pecans using a spatula or wooden spoon.
Take about 2 tablespoons of the dough and shape it into balls (1 tablespoon for a smaller cookie)
Place onto a cookie sheet lined with parchment paper and space 3 inches apart.
Bake the cookies for 9 to 10 minutes. If you’re making a smaller cookie, reduce the time to 6 to 7 minutes.
Remove the cookies from the oven and allow them to cool on the baking sheet.