Cream together butter and sugar until light and fluffy.  Add egg yolks and vanilla.  Beat well.
    Add flour sifted with baking powder.  Mix thoroughly.  Chill dough for several hours.
    Roll dough about 1/4 inch thick on floured pastry board.  Cut rounds about 2 1/2 inches in diameter.
    Cut smaller rounds or stars into centers of half of the cookies.
    Bake at 350 degrees for 10 minutes or until very lightly browned.  When cooled, spread jam on the
    bottoms of the whole cookies and dust the tops of the others that have the cutouts with confectioners
    sugar.  Place sugar coated cookies on top of jam spread cookies.  Makes about 28 filled cookies.