Preheat the oven to 325 degrees F.
In a medium bowl, combine the flour, salt, cornstarch, and unsweetened cocoa powder. Set aside.
Add 1/2 cup of confectioners sugar to a different (small) bowl, and set aside. for later.
Next, add the softened butter and one cup of confectioners sugar to a mixing bowl. Using an electric mixer on medium speed, cream until light and fluffy. Then, mix in the vanilla extract.
Gradually add the flour mixture to the creamed mixture and mix just until combined. Stir in the finely chopped pecans.
Shape the cookie dough by the tablespoon into balls approximately 1 inch wide.
Line them up on an ungreased cookie sheet(s), about 2 inches apart. You can line the sheets with parchment paper if you'd like.
Bake for 12-14 minutes until done.
For the final step, use a pastry brush to apply confectioners sugar to the warm cookies. (Or if you prefer, you can roll them in the bowl of confectioners sugar and tap off the excess.)
Store the cooled cookies in an airtight container.