Preheat your oven to 325 degrees Fahrenheit. Cut your lamb shoulder into small, even two-inch chunks. Pat the meat dry with a clean paper towel first.

Heat oil in your frying pan over high heat. Brown the lamb chunks in batches until they are golden. Remove the meat and set it aside on a plate.

Add the sliced onions and carrots to the same pan. Cook them slowly until they are soft and look translucent. Stir in the flour and cook for two more minutes.

Pour in the lamb stock and the Worcestershire sauce slowly. Add the fresh thyme and bring the liquid to boil. This creates the base for your rich hotpot gravy.

Layer the meat and vegetables in your casserole dish. Peel and slice your potatoes into very thin round circles. Arrange them on top like shingles on a roof.

Brush the potatoes with melted butter and some salt. Cover with foil and bake for ninety minutes total. Remove the foil for the last thirty minutes to crisp.