Mix the flour with the salt in a large bowl. Add the butter and rub it into the flour with the tips of your fingers, until it resembles fine crumbs.
Stir in the milk with a round blade knife (butter knife) to make a soft but not sticky dough.
Turn out onto a lightly floured work surface and shape into a soft, smooth ball.
Set the ball of dough onto a tray or baking sheet and flatten gently to make a round about 17 cm across. Cut a deep cross in the dough and brush lightly with milk.