1& 1/2 cups all purpose flour
1/4 teaspoon salt
2/3 cup butter (room temperature)
1/3 cup white sugar
2 egg yolks
1 teaspoon vanilla extract
2 egg whites, slightly beaten
3/4 cup finely chopped pecans or walnuts
1/3 cup favorite jam
Beat the butter for 30 seconds; add sugar and beat until light and fluffy. Add egg yolks and vanilla, mix well. Stir dry ingredients together and add to to butter mixture, beat until well blended.
Shape pieces of dough into one inch balls and coat them with egg whites and then roll them in chopped nuts. Place them on a UNgreased cookie sheet and use your finger to make an indentation in the center of the cookie (I know it says "thumbprint" but your finger works better lol). Set the cookie sheet in the fridge to chill for half hour or so (or freezer for 15 minutes).
Bake for 17-20 minutes in preheated 350 oven, or until golden. Cool on wire rack. When the cookies are cool, fill the depression with 1/4 teaspoon of your favorite jam.