My husband’s mother used make these all the time when he was growing up. When I met him, many, many years ago, I had never had them. The first time I tasted them I could tell why he liked them so much. They are good. And such a special cookie for the holiday.
Preheat oven to 350.
In large bowl, cream butter and sugar. Beat in egg yolk, almond extract, and salt. Blend in flour gradually.
Pinch off pieces of dough and roll into one-inch balls. (if necessary, chill the dough for 30 minutes or until firm)
Dip each ball in beaten egg white to coat, then roll in finely chopped walnuts.
Arrange balls on ungreased cookie sheets, spacing about one inch apart. Use your thumb to make an indent in the center of each cookie.
Bake cookies one sheet at a time for 10 to 12 minutes or until pale golden. Remove from oven and gently press the centers again. Let cookies cool on racks.
Neatly fill each hollow with about 1/4 tsp jam.