Preheat the oven to gas mark 4, 180°C, 350°F. Place the seasoned flour on a plate and roll the cubes of lamb in the flour to coat. Heat the oil in a large pan and add the seasoned meat and brown.
Add the rosemary, leeks and seasoning, heat through and add the stock, bring to the boil and then turn off the heat and prepare the pastry.
In a bowl mix together the flour, rosemary and suet. Add a few spoonfuls of cold water and mix together with a spoon. If the mix doesn't come together add a little more water. Using your hands press the mixture together to form a ball.
Place pastry on a board and roll out to a thickness of about 1-2cm. Lightly grease with a little oil a 1.1 litre/2pt heat resistant pudding bowl and then line with non-stick baking paper
Add the pastry and line the bowl - either let the pastry fold over at the top or roughly pull off to re-roll for the lid.
Add a large spoonful of the meat mixture to the lined bowl and then place the whole apple on top, finish off by adding the remaining meat and fill almost to the top with the juices
Fold the pastry over at the top and/or seal with the pastry lid. Press the pastry together to seal the top. Cover with a piece of non-stick baking paper and then a layer of foil.
Place pudding in a deep roasting tin and pour a little hot water into the tin to come about 5cm up the pudding bowl. Cover with foil and place in a preheated oven for 1½ - 2 hours, until pastry is risen slightly and starting to brown
Remove carefully from the oven, allow to stand for about 5 mins and then turn out onto a large plate.
Serve with extra seasonal steamed green vegetables.