Preheat the oven to 180°C. Line a baking sheet with baking paper.
1. Pastry: Put the flour and salt in the bowl of a food processor, add the butter and pulse until the mixture resembles bread-crumbs.
2. Add the egg and half the milk and pulse until the dough starts to bind. Add the rest of the milk little by little until a dough forms. Remove the dough and knead lightly. Shape into a ball, cover with cling film and chill in the fridge for at least 30 minutes.