Preheat oven to 325˚F (165˚C).
Cream butter; add sugar and beat well. Then beat in egg yolk and salt.
Gradually stir in flour to make a soft dough.
Divide dough into three pieces. Roll out each piece into a 11 cm x 30 cm (4 ½” x 12”) rectangle. Cut off two strips 2 cm x 30 cm (1” x 12”). Dampen edges of the remaining 7 cm x 30 cm (2 ½” x 12”) rectangle. Carefully slide a narrow strip onto each edge.
Cut the rectangle strip diagonally into 1” cookies. Lift the cookies gently with a metal spatula onto greased cookie sheets. Bake for 18 – 20 minutes or until lightly browned. Let cool slightly on baking sheets, then cool on racks.
Spread raspberry jam into the indentation along the middle of each cookie. Spread vanilla icing on the edges (a piping bag can also be used.) Or simply sprinkle edges of cookies with icing sugar.