Last Updated on 2021-01-09 by Audie Casiguran
Preheat oven to 350 degrees.
Stir together flour and salt. Beat butter for 30 seconds; add sugar and beat until fluffy. Add egg yolks and vanilla; beat well. Add dry ingredients to beaten mixture, beating until well blended. Cover and chill 1 hour.
Shape into 1-inch balls; roll in egg whites, then roll in finely chopped walnuts. Place 1-inch apart on an ungreased cookie sheet. Press down centers with thumb. Bake for 15-17 minutes. Cool on a wire rack. Just before serving, fill centers with preserves.