Sieve together the flour and the salt, then rub the butter and the flour together with your fingertips. Add the egg and the milk and mix together. When they are mixed in, knead the pastry into a smooth dough, but do not overwork; the finished dough should be quite firm.
Wrap in greaseproof paper or in a polythene bag and store in the refrigerator. Allow to rest for at least an hour before using.