In a large bowl, beat butter and confectioners' sugar until blended. Beat in egg yolk and extract. Gradually beat in flour. Refrigerate, covered, at least 2 hours or until firm.
Preheat oven to 350°. Shape into 3/4-in. balls.
Place 1 in. apart on greased baking sheets. Press a deep indentation in center of each with your thumb.
Bake 12-14 minutes or until edges are light brown.
Remove from pans to wire racks. Fill each with 1/4 teaspoon preserves; cool completely.
