You can easily make melt in the mouth crispy (on the outside), tender (on the inside), shredded roast lamb at home. The most important ingredient is the quality of the meat. Go to a good local butcher and get a decent 2-3kg joint if you can. Somewhere like Ginger Pig is up there with the best but go with the best you can get for your budget.
Prepare the lamb simple by making cuts into the flesh and inserting garlic cloves (whole with skin on) and fresh rosemary into the cuts. Rub with a bit of olive oil and the generously season with salt and pepper.
Place in a deep oven tray and set your oven pretty much as hot as it can go around 220 degrees C. You want to brown the skin on the outside for about 20 mins or until it has reached a nice brown colour. Then turn the oven down to 160 degrees. At this point take the tray out, add 1/2 a bottle of red wine and a glass of chicken stock or water and cover the tray with aluminium foil tightly so that no steam can escape. You then leave it for 5-6 hours preferably but 4 hrs at the very minimum. You can check it every couple of hours just to see where the liquid level is but it should gently steam and keep moist if you have wrapped it tightly in tin foil.
After the meat is cooked leave it to rest for 30-45 minutes.
This gives you time to finish the rest of your vegetables and gravy. Reduce the cooking liquids and add a small amount (1 teaspoon) of cornflower dissolved in cold water if the gravy isn’t thick enough for your liking. Roast potatoes cooked in hot goose fat, garlic and rosemary or potato dauphinoise go well as well as some crunchy green veg such as sauteed savoy cabbage, spinach, kale, green beans or tender stem/purple sprouting broccoli.