In a small bowl, cream butter and sugar. Beat in egg yolk and vanilla. Combine the flour and salt; gradually add to creamed mixture. Cover and refrigerate for 1 hour or until easy to handle.
In a small bowl, beat egg white. Place coconut in another bowl. Roll dough into 1-in. balls; roll in egg white and coconut. Place 2 in. apart on ungreased baking sheets. Using the end of a wooden spoon handle, make an indentation in the center of each.
Bake at 325° for 19-22 minutes or until lightly browned. Remove to wire racks. Spoon 1 rounded teaspoon of preserves into each warm cookie. Dust with confectioners' sugar. Cool completely. Yield: about 2 dozen.