Preheat the oven to 220 degrees C (430 degrees F).
Place the garlic cloves in a large, heavy-based casserole dish. Season the lamb with salt and freshly ground black pepper and place it on top of the garlic. Roast the lamb in the oven, uncovered, for 10 minutes. Turn the lamb over and give it another 10 minutes on the other side. Remove the casserole dish from the oven.
In a saucepan over medium–high heat, bring the buttermilk to the boil. Add the thyme and bay leaves and pour the mixture over the lamb. Cover with a very tight-fitting lid or piece of aluminum foil. Reduce the oven temperature to 140 degrees C (275 degrees F). Return the casserole to the oven and bake until the meat is soft and tender (3–4 hours). Make sure to baste every 30 minutes with the pan juices during cooking.
While the lamb is cooking, prepare the pears (see below)
Peel the potatoes and halve them lengthways. Place one potato, cut side down, on a board and make thin, evenly spaced cuts at 1-millimeter (1/16-inch) intervals, about two-thirds of the way through. Repeat with the remaining potatoes.
With 1 hour to go, add the potatoes, with the fins facing up, to the tray with the lamb and re-cover. In the final 30 minutes, remove the cover and turn the oven up to 220 degrees C (430 degrees F). Using a spoon, position the curds onto the lamb for them to caramelise for the rest of the cooking time. Baste the potatoes with the lamb juices and bake until crisp. This is also the time to place your pears in the oven. They will take about 30 minutes to bake until golden brown and soft.
After the final 30 minutes, check to see that everything is cooked. Remove the lamb from the pan and strain the whey sauce and caramelized buttermilk curd. Tear off a piece of lamb flesh for each serving, and include a couple of roast potatoes and a lovely roast pear. Spoon over some curd and a ladleful of whey to moisten.