Preheat the oven to 150°C/Gas mark 2.
Pour 2 tablespoons of vegetable oil onto a large roasting tray and place over a high heat until the oil is smoking.
Generously season the ribs with salt and pepper and sear and colour until golden brown, remove from the roasting tray and drain in a colander (cook these in batches to avoid crowding the pan).
Heat a further 2 tablespoons of oil in the same roasting tray, then add the roughly chopped carrots and onions, leeks, thyme, peppercorns, garlic and bay leaves.
Cook for 10–12 minutes until the veg is nicely soft and browned.
Pour the Guinness into the pan and leave to reduce by half (around 5 minutes), then return the ribs to the tray and barely cover with beef stock and Worcestershire sauce. Cover with foil and place in the oven for around 4½ hours, turning every hour until the meat is tender and is falling off the bone.
Carefully remove all the meat and bones from the pan and set to one side. Pass the cooking liquid through a fine sieve and pour into a clean pan.
Place on a medium heat and bring to the boil.
Skim and reduce by half (around 20 minutes; this should give you around 750ml).
Allow the ribs to cool, then pick off all the meat, shred and chop finely into a large bowl.
Place a saucepan over a medium heat, add a tablespoon of vegetable oil and then the sliced onions, sprinkle over a tablespoon of brown sugar and caramelise for 10–15 minutes. Add in the cubed carrots and cook for a further 8 minutes until slightly softened, stirring occasionally.
Add the caramelised onions and carrots to the bowl of meat, then combine with the reduced cooking liquor.
Season, then place the mixture into either individual dishes or one large dish. Leave to one side and allow to cool.
Increase the oven temperature to 190°C/Gas mark 5.
Place the chopped potatoes in a large saucepan, cover with cold water, season with salt and bring to the boil.
Cook until tender, then drain thoroughly in a colander.
Place back in the saucepan over a low heat, add the butter, milk and double cream and season with salt, then mash together.
Place in a piping bag and pipe on top of the cottage pies (alternatively, just spoon on carefully and fluff up with a fork).
Sprinkle the grated cheese over the top.
Place in the oven and cook for 15–20 minutes until golden brown.
Garnish with spare rib bones (optional).