For the tatties
Boil the peeled potatoes in water until soft, then drain and mash. Heat the cream and add to the mashed potato. Mix in the cold butter and beat until emulsified. Season with salt to taste.
For the roast lamb
Trim any fat off the meat. Heat the olive oil in a frying pan, add the meat and brown on both sides. Add the butter, chopped garlic and herbs and baste the meat in these flavours. Place the basted lamb into a roasting tin and cook in a preheated oven for 10 minutes at 200°C/400°F/Gas mark 6.
For the neeps
Boil the turnip in water until soft. Cool and reserve for later. Cook the shallot in the butter until caramelised and also reserve for later.
For the lamb neck terrine
Brown off the lamb neck in a frying pan and place into an ovenproof dish. Add all the chopped vegetables and wine and braise in the oven at 160°C/325°F/Gas mark 3 for 5 hours. Once cooked, remove the neck from the liquid and allow to cool slightly. Slice the neck into bite-size pieces and mix into a paste with the haggis. Season by adding the chopped herbs and add a few spoons of the liquor to bind the mixture together; the mixture should be firm. Put the mix onto a baking tray and flatten to approx 2.5cm thick. Set in the fridge. When set, take the meat out of the tray and cut into squares about 15cm x 15cm. Dip into the flour then the egg-wash and coat in breadcrumbs. Reserve until needed. Sieve the remaining braising liquid and place into a pan and reduce to a sauce consistency.
Reheat the turnip and onion in the sauce. Deep fry the braised neck at 170°C/350°F/Gas mark 4 until golden. Carve the sliced loin.
On a plate, sit the crispy terrine in one corner. Pipe mashed potato on top, opposite the carved neck with three squeezes of turnip and onion. Drizzle all the sauce and serve.