Beat butter and cream cheese at medium speed of an electric mixer, until creamy. Gradually add sugar beating well. Add egg yolk and almond extract, mixing well. Gradually stir in flour. Cover and chill 1 hour. Shape dough into 1-inch balls. Roll balls in lightly beaten egg white, and then in almonds. Place 2 inches apart on greased cookie sheets. Press a cherry half in center of each ball. Bake at 350 degrees for 15 minutes. Remove to wire racks to cool.