Preheat your oven to 350°F and generously butter a 9x13 inch casserole dish. The butter prevents sticking and adds richness to the bottom layer of potatoes.
Pat the lamb chunks dry with paper towels, then season generously with salt and pepper on all sides. Dry meat develops better flavor, and seasoning now means every bite of lamb will be properly seasoned.
Arrange half the potato slices across the bottom of your prepared dish, overlapping them slightly like fallen dominoes. This foundation layer will absorb the lamb juices and become incredibly flavorful.
Distribute the seasoned lamb chunks evenly over the potatoes, then scatter the sliced onions on top. The onions will soften and sweeten as they cook, creating natural flavor bridges between the lamb and potatoes.
Sprinkle the thyme leaves over everything if using, then season the whole assembly with the remaining salt and pepper. The herbs will perfume the entire dish as it slowly braises.
Create the signature top crust by arranging the remaining potato slices in overlapping rows, like roof shingles. Take your time here — neat, even rows will give you the most beautiful golden presentation.
Pour the warm stock carefully around the edges of the dish, avoiding the top potatoes completely. Dot the potato surface with butter pieces. The stock should come about halfway up the sides — it will create steam and eventually reduce to a rich gravy.
Cover tightly with aluminum foil and slide into the oven for 90 minutes. This covered phase gently steams everything together, tenderizing the lamb while the bottom potatoes absorb all those savory juices.
⏱ 1 hr 30 min
Remove the foil and continue baking until the top potatoes turn deep golden brown and slightly crispy at the edges, about 30 minutes more. You want real color here — that's where the flavor lives.
⏱ 30 min
Let the hotpot rest for 10 minutes before serving. This settling time allows the bubbling juices to calm down and makes serving much cleaner, plus the flavors will be perfectly melded together.
⏱ 10 min