Untwist the sausage links and wind them round into a Catherine wheel. Push two skewers through the spiral to secure. Poke in the bay leaves and brush with 1 tablespoon of oil, then transfer to a baking tray and cook for 35 to 40 minutes, or until golden and crispy.
Peel and halve the potatoes, then cook in boiling salted water for 15 minutes, or until tender. Drain, then return to the pan and cover
Meanwhile, heat the milk gently in a pan. Roughly chop half of the watercress and trim and finely chop the spring onions. Add them both to the milk and simmer for 5 minutes, or until softened.
Add the cooked potatoes to the milk and mash until smooth. Season well with sea salt and black pepper, then cover with a lid and keep warm.
To make the gravy, peel and finely slice the onions. Add the butter to a pan over a medium heat and fry the onion and rosemary for 5 minutes, or until the onions are sweet and translucent. Stir in the flour, then add the stock and cider, and simmer until reduced to a thick, tasty gravy.
Serve the sausage with the mash, gravy and remaining watercress.