Cream the butter. Beat in the sugar, salt and vanilla. Stir in 1 cup of flour and as much extra flour as needed to make a stiff dough.
Shape into balls and put a thumbprint on top and place on an ungreased baking sheet. Bake in a 350 °F. oven for 12 to 15 minutes, or until lightly browned.
Filling (fill while still warm)
Spoon filling into depression on top of cookies.
Heat together until chocolate is melted. Stir until smooth.
Stir in: 1/2 cup powdered sugar and beat until smooth.
Drizzle over top of the filled cookies.