preheat oven to 350
mix butter, shortening, sugar, egg yolk and vanilla until light and fluffy
work in flour and salt until dough holds together
shape into 1 inch balls
beat egg white slightly
dip each ball into egg white and roll into the nuts
place 1 in apart on ungreased baking sheet press thumb deeply into the center of each
bake for 10 min or until lightly brown
immediately remove from baking sheet and cool
fill thumbprints with jelly, jam, or frosting etc...