1. Roll out the pastry into a large circle, 2.5 cm (1 inch) larger all round than the top of a 1.5-litre (2 1/2-pint) pudding basin.
2. Cut out a quarter of the pastry for the lid.
3. Grease the pudding basin and dust the pastry with flour. Lift the pastry into the basin and press into the base and up the sides. Put half the butter, cut up into pieces, into the centre, with half the sugar. Prick the lemon all over with a skewer.
4. Put the fruit on top of the butter and sugar. Add the remaining butter and sugar. Dampen the pastry edges and cover with the pastry lid, sealing the edges well.
5. Cover with greased greaseproof paper and foil and steam for about 4 hours.