Preheat your oven to 325°F (160°C).

Toss the lamb chunks in the seasoned flour until lightly coated, shaking off any excess.

Heat the vegetable oil in a large skillet over medium-high heat and brown the lamb on all sides. Remove the meat and set aside.

In the same skillet, add the sliced onions and cook for 5 minutes until soft and slightly golden.

In a deep casserole dish, arrange a layer of half the browned lamb, followed by half the onions, carrots, and parsnips. Season lightly with salt, pepper, and thyme leaves.

Repeat the layering with the remaining meat and vegetables, tucking the bay leaf into the center.

Mix the stout beer, stock, and Worcestershire sauce together, then pour the liquid over the meat and vegetable mixture.

Arrange the sliced potatoes in an overlapping scale pattern over the top of the filling, covering it completely.

Brush the tops of the potatoes generously with the melted butter.

Cover with a tight-fitting lid or foil and bake for 60 minutes.

Remove the lid or foil, increase the oven temperature to 400°F (200°C), and bake for another 30-40 minutes until the potatoes are golden brown and crispy.