2/3 cup butter
1/3 cup white sugar
2 egg yolks
1 teaspoon vanilla extract
1/2 teaspoon salt
1 1/2 cups all-purpose flour
2 egg whites, lightly beaten
3/4 cup finely chopped walnuts
1/3 cup strawberry preserves
Preheat oven to 350 degrees.
Lightly grease cookie sheets, or line with parchment paper.
In a large bowl, cream together butter and sugar until light and fluffy.
Beat in egg yolks, vanilla, and salt.
Gradually mix in flour.
Shape dough into 3/4 inch balls.
Dip in lightly beaten egg whites, then roll in finely chopped walnuts.
Place 1 inch apart on prepared cookie sheets. Press down center of each with thumb.
Bake for 15 to 17 minutes, or until golden brown. Cool on baking sheet for 5 minutes, then remove to a wire rack to cool completely.
Just before serving, fill centers of cookies with strawberry preserves.