The fillings for both are similar; it is the way the filling is cooked that differs. Steak and kidney pudding is always made with a suet-crust pastry, and the uncooked mixture is spooned into the pastry before the pudding is steamed. For a steak and kidney pie, the meat filling is usually cooked before being put into a pie dish which is then covered with pastry and baked. Sometimes the filling is cooked under the pastry and, on these occasions, rump steak is used.
The traditional pastry used for a steak and kidney pie is suet-crust pastry but puff, flaky or short crust pastry are equally popular today, and give deliciously good results.