Preheat the oven to 220 degrees C. Line a baking tray with baking paper. Rub the butter into the flour, until the mixture resembles breadcrumbs. Stir in the sugar and salt.
Make a well in the centre of the mix and stir in the milk. Stir until the mixture is even and the dough comes together. Turn out onto a floured surface then shape into a rough square about 3-4cm thick.
Transfer to the prepared baking sheet. Brush all over with milk and score into nine rough squares. Bake for 15 minutes until golden and cooked though. Cool on a wire rack. Serve warm or cold.