In a large bowl cream together the butter, salt, sugar, egg yolks and vanilla seeds. Add flour all at once and knead mixture quickly, until a ball of dough is formed. Wrap tightly with cling film and put in fridge to chill for at least 1 hour.
Preheat oven to 180 C / Gas 4. Lightly grease a baking tray, or line with baking parchment.
Roll out dough with a rolling pin to a thickness of about 5mm. Cut biscuits out of dough using your favourite biscuit cutter shapes.
Bake on prepared baking tray for about 10 minutes, then let cool and enjoy!