1. Preheat oven to 300 degrees. Grease cookie sheets or line with parchment paper
2. Separate egg. Place egg white in small, shallow bowl and set aside.
3. Place chopped walnuts in another small, shallow bowl and set aside.
3. Cream butter, sugar, vanilla, and egg yolk in mixing bowl on medium speed.
4. Slowly add in flour and salt
5. Spray hands with Pam or rub in butter. Shape dough into ping-pong size balls. Roll in egg white, then in walnuts. Place on cookie sheets about 2 inches apart. Bake for 5 minutes.
6. Remove from oven. With thumb, dent each cookie. Put apple butter in each thumb well.
7. Put back in oven and bake another 6 - 8 minutes until cookies are done.