For the suet crust, put the flour and suet into a bowl. Measure the milk in a jug and then add 75ml/2½fl oz cold water to make 150ml/5½oz of total liquid. Add this to the suet and mix to make a soft dough.
Lightly dust the work surface with flour and then roll out the dough to a 30cm/12in circle. Cut one-quarter out of the circle and set aside for the lid. Thickly butter the pudding basin and then line with the pastry, pressing the join together.
For the filling, peel and core the apples, then cut them into cubes and mix together in a mixing bowl with the butter and sugar. Place a little of this mixture in the pudding basin on top of the suet pastry. Prick the lemon all over with a cocktail stick and then place it in with the apples so that it sits upright. Pack the remaining apples and butter mixture around the lemon.
Roll out the reserved suet pastry to a circle to fit on top of the pudding, trim any excess pastry and pinch the edges to seal.
Cut a square of foil and make a pleat in the centre. Tie the foil around the basin with string, then loop the string over the basin and back under the string a couple of times to make a handle. Tie securely.
If you don’t have any string, fold a long strip of tin foil horizontally in half – and then half again. Place the foil around the bottom of the basin, and wrap the sides up and around to act as support as the basin is lowered into the pan.
Place the lid of a jam jar in the large saucepan to stop the basin touching the bottom of the pan.
Add the pudding basin to the pan and then pour boiling water around it so that it comes three-quarters of the way up the side of the basin. Cover with a tight-fitting lid, and simmer for 3½ hours. Check occasionally and top up with more boiling water as necessary.
To serve, remove the foil and invert the basin onto a large serving plate. Remove the basin and serve in slices with cream or custard.