Step 1
Preheat oven to 180C/160C fan forced. Grease a 3.5cm-deep, 24cm round pie dish. Line with pastry and trim off excess. Crimp the top edge. Transfer to the fridge until required.
Step 2
Meanwhile, place the buttermilk, sugar, butter, eggs, flour, juice, vanilla and salt in a food processor. Pulse until the mixture is smooth and well combined.
Step 3
Place the dish on a baking tray and pour the buttermilk mixture into the pastry shell. Transfer to oven and bake for 40-45 minutes (place foil around the edge of the pastry if browning too quickly) or until top is golden and filling is just set in the centre (it will still wobble slightly). Set aside for 1 hour to cool slightly then transfer to the fridge for 2-3 hours, or overnight, until filling has chilled and set. Cut into wedges and serve.