1. Score the fat around the leg of lamb in a criss-cross pattern, drizzle with a little olive oil, then rub all over with salt and pepper. Place in a deep roasting pan and scatter with garlic and thyme over and around. Pour over the lemon juice and drizzle again with olive oil. Sprinkle with a little more seasoning, then roast in the hot oven for 20 minutes.
2. Slice the apples in quarters and cut off the cores. Remove the lamb from the oven and reduce the heat to 180c/gas 4. Scatter the apples around the pan and baste the lamb with the cider. Turn the lamb over and drizzle with 2 tablespoons of honey. Return to the oven for 30 minutes.
3. Turn the lamb round, baste the meat with the pan juices, then drizzle over another tablespoon of honey. Continue to roast for the calculated time.
To check, insert a skewer into the thickest part of the lamb, then press the meat lightly: the redder the juices the rarer the meat. Lift the lamb to a carving board and cover with a piece of foil. Rest in a warm place while you prepare the gravy.
4. At this point, the apples and garlic in the roasting pan should be very soft. Press with a fork, then tip the entire contents of the pan into a fine sieve over a saucepan. Push down with the back of a ladle to extract all the juices and flavour from the apples and garlic. Discard the pulp.
5. Place the saucepan over a medium heat and add the stock. Bring to the boil and let it bubble vigorously until the sauce has thickened to a desired gravy consistency. Taste and adjust the seasoning, then pour into a warm serving jug.
Carve the lamb into thin slices and serve drizzled with the apple and cider gravy.