Start with the colcannon. Place the potatoes in a pan with enough cold water to cover. Bring to a boil then simmer for 15 minutes, until the potatoes are tender.
Whilst the potatoes are cooking, place the kale and spring onions in a small pan. Add a good splash of water*, place a lid on and place on a high heat for 3 minutes - until just softened. Remove from the heat and drain.
Once the potatoes are tender, drain off the water, then mash the potatoes using a masher or a potato ricer. Stir though the butter, cream, salt and pepper, then stir in the cooked kale and spring onions, Put to one side.
Heat the oil in a large frying pan and add the sausages. Brown on all sides on a high heat, then turn down to a medium heat. Remove the sausages and add the sliced onions. Cook the onions, moving around the pan regularly for 10-15 minutes until browned and caramelized.
Stir in the flour using a whisk and cook for 1 minute, then add the stock a little at a time, whilst stirring with the whisk, until you have a thickened gravy. Add the sausages back into the pan, along with the mushrooms, peas, Worcestershire sauce, bay leaf and a pinch of salt and pepper. Stir everything together, then transfer to a baking dish (approx 30cmx30cm).
Top the mixture with the colcannon, and ruffle the top with a fork (this helps to get some brown crispy bits on top). Place in the oven to cook for 20-25 minutes until bubbling at the edges and starting to brown on top.
* For a more traditional colcannon, you can boil the kale and spring onions with whole milk instead of water, then use the milk instead of cream in the mashed potatoes. I just prefer to use cream in my mashed potatoes..Nutritional Information is per serving.