Preheat the oven to 180C/350F/Gas 4.
Place the red onions, carrots and turnips into a heavy-based lidded casserole dish. Add the lamb and bay leaf and season with salt and freshly ground black pepper.
Cover the lamb and vegetables with the black pudding slices followed by a layer of potato slices, overlapping the slices to completely cover the lamb, vegetables and black pudding.
Add the hot stock to the casserole and brush the potatoes with melted butter.
Cover the casserole and place in the oven to cook for about two hours. After two hours remove the lid and cook for another 30-45 minutes, until the potatoes are crisp and golden-brown.
Take the casserole dish to the table and serve.
