Line 23 cm pie pan with pastry; refrigerate until used. Mix sugar, flour, salt and cinnamon; add to apples and mix thoroughly. Set aside. Crush pears and spread in bottom of pastry-lined pan; sprinkle with rum. Heap apple mixture over pears; dot with butter. Put on top crust; seal and crimp edges; cut slits for steam to escape.
Bake at 200ºC for 45 minutes or until apples are tender. Serve warm.