1In large bowl, beat butter and sugar with electric mixer on medium speed until light and fluffy. Beat in egg yolks and almond extract. On low speed, beat in flour and salt until blended. Cover; refrigerate 1 hour.
2Heat oven to 350°F. Shape dough into 1-inch balls. In small bowl, slightly beat egg whites. Dip each ball in egg whites; roll in pine nuts, pressing to adhere. On ungreased cookie sheets, place balls 2 inches apart. Press thumb in center of each ball to make indentation.
3Bake 13 to 15 minutes or until light brown. Cool 2 minutes; remove from cookie sheets to cooling racks. While still warm, press centers of cookies with thumb. Cool completely. Spoon about 1/2 teaspoon jam into each indentation.