Cream butter and sugar. Add the egg and vanilla and beat to a creamy consistency.
Sift flour with the salt and add to the butter mixture. Add the oatmeal, mixing well. Chill.
Shape into small balls and roll in the coconut. Make a good-sized dent on top of each ball.
Bake on ungreased cookie sheets in a preheated slow oven, 275 degrees, for 30 minutes. Remove and let cool. Fill the dented centers as follows:
Chop the prunes, add sugar and cook until thick. Cool, and fill the centers of the cookies.
Warm your oven, turn off heat, and put cookies in to dry out for a few minutes.