Split the vanilla pod in half lengthways and scrape out the seeds with the tip of the knife into a bowl. Add the eggs and beat lightly.
Beat the butter and sugar together using an electric mixer until smooth and creamy. Gradually work in the beaten egg, a little at a time. Sift the flour and salt together and slowly add to the mixer. Beat on low speed until all the flour is incorporated; stop as soon as the dough comes together.
Using floured hands, tip the dough out onto a lightly floured surface and press together gently to form a ball. (Don't knead the dough or it will become tough). Flatten the ball and lightly roll out to 1cm thick circle. Using a 20cm plate as a guide, trim to a perfect circle. Carefully lift onto a baking tray lined with baking parchment. (Re-roll the trimmings to make smaller biscuits if you like.)
Using a large knife, score the dough into 8 sections without cutting all the way through, then lightly press 2 dimples on the edge of each wedge with your thumb. Cover loosely and chill for at least an hour to firm up.
Preheat the oven to 160°C/Gas 3. Remove the shortbread from the fridge and bake for 30-40 minutes until the biscuit is firm and a pale golden colour. Leave on the baking tray for a minute then, using a palette knife, lift onto a wire rack to cool. Sprinkle with caster sugar whilst it is still warm.
Once cooled, break along the indentations into wedges and store in an airtight tin until ready to serve.
Recipe from Gordon Ramsay - Christmas with Gordon