1. Put nuts in a 9-inch cake or pie pan. Bake in a 350° oven until pale gold under skin, 10 to 12 minutes. Pour nuts into a towel and rub briskly with the cloth to remove as much skin as possible. Lift nuts from towel and finely chop. Wipe out pan.
2. Cut butter into chunks and put in a large bowl. Beat with a mixer on high speed until fluffy. Add 1/3 cup of the powdered sugar and the vanilla; beat on slow speed to incorporate, then beat on high speed until fluffy.
3. On low speed, mix in flour and salt, then beat until blended.
4. Stir in nuts.
5. Shape dough into 1-inch balls. Place about 2 inches apart on baking sheets.
6. Bake in a 300° oven until cookies no longer feel soft when gently touched but are not browned, about 18 minutes. (If using one oven, alternate pan positions after 8 to 10 minutes.) Cool on pans about 5 minutes.
7. Place remaining powdered sugar in cake pan. Gently roll hot cookies, a few at a time, in sugar to coat well. Set cookies slightly apart on piece of waxed paper (about 20 in. long) until almost cool, then roll in sugar again. Return cookies to paper in a single layer. Shake cocoa through fine strainer over cookies. Let cookies cool.
8. Serve, or store airtight at once for up to 3 days. Freeze to store longer.
Nutritional analysis per cookie.