Using a mixer on medium-low speed, cream together butter and sugar. Add in vanilla.
Add in the salt and cocoa.
Gradually add in the flour, and mix until well-combined.
Reduce the mixer to low and add in the pecans, or fold in by hand. Refrigerate dough for at least one hour.
Preheat oven to 350F.
Roll dough into 1" balls and place 1" apart on greased cookie sheet. Bake 12 minutes.
Cool completely and roll in powdered sugar.