Preheat your oven to 325°F (160°C). Heat 1 tablespoon of vegetable oil in a large ovenproof casserole dish or Dutch oven over medium-high heat.

Season the lamb chunks generously with salt and pepper. Brown the lamb in the hot oil for 5-7 minutes, turning occasionally until a golden-brown crust forms on all sides, then transfer the meat to a plate.

Add the remaining 1 tablespoon of oil to the same pan, then add the thinly sliced onions and carrots. Sauté for about 5 minutes until the onions are softened and slightly translucent, scraping up any browned bits from the bottom of the pan.

Sprinkle the flour over the vegetables and stir well to coat, cooking for 1 minute to cook off the raw flour taste. Gradually pour in the beef broth, stirring constantly to prevent lumps, then add the thyme, Worcestershire sauce, and the browned lamb back into the pan.

Bring the mixture to a gentle simmer, then remove the dish from the heat. Carefully arrange the thinly sliced potatoes in overlapping concentric circles over the top of the meat and vegetables, completely covering the stew below.

Brush the melted butter evenly over the top layer of potatoes and season with a little extra salt and pepper. Cover the dish with a tight-fitting lid or a double layer of aluminum foil.

Bake in the preheated oven for 1.5 hours. Remove the lid or foil, increase the oven temperature to 400°F (200°C), and bake for another 30 minutes until the potatoes are tender on the inside and deeply golden and crispy on top.

Remove from the oven and let the hotpot rest for 10 minutes before serving. Serve hot with a side of pickled red cabbage or steamed green beans for a truly traditional British pub-style meal.