Mix together the flour, butter, egg yolk, icing sugar, vanilla sugar, salt and grated lemon rind to form a dough. Leave the dough in a cool place for an hour.
Out of the dough make small balls and place on a prepared baking tray. Make a small indentation in the middle of each ball, using your little finger and fill the hole, using a teaspoon, with raspberry jam.
Bake your cookies at 200 degrees C for about 15 minutes.
Leave them to cool and then coat the bottom of each cookie with melted chocolate and leave until firm.