1 Heat the oven to 180C fan assisted / 200C conventional / 400F / gas mark 6 and line a cookie sheet with baking parchment.
2 Beat the butter with the icing sugar, salt and vanilla bean seeds and add the egg white. Beat until the mixture is light in colour.
3 Mix together the flour, nuts and corn starch and stir into the butter mixture.
4 Spoon the dough into a piping bag with a star nozzle.
5 Pipe approximately 2" long portions of dough onto a cookie sheet and bake for 12-15 minutes until golden. Remove from the oven and let cool.
6 To decorate, melt the chocolate over simmering water. Dip the cookies half into the chocolate, place on baking parchment and leave to set.