Preheat oven to 150°C. Lightly grease a large baking tray.
In a large bowl cream together butter, caster sugar, vanilla essence and salt until pale in colour (can be done by hand or in an electric mixer).
In a separate medium bowl mix together flour and cornflour, then sieve into butter mixture. Add hemp seeds and mix quickly and thoroughly to bring all ingredients together – but don't over-mix as you run the risk of warming the shortbread mixture, which will result in a poor crumb.
Turn out onto a lightly floured work surface and knead gently and quickly to form a loose dough. Place dough between 2 sheets of greaseproof paper and roll out to 1cm thick. Cut into desired shapes using cookie cutters then transfer to a baking tray.
Bake for 15 minutes at 150°C then turn oven down to 130°C and continue baking for 10-15 minutes or until pale and crisp.
Remove from oven and carefully transfer to a wire rack to cool.