Preheat oven to 175oC.
Lightly wet the pork with oil then season with SIDS SALT & PEPPER, SIDS CRAZY SALT, paprika and caraway seeds then spread SIDS FENUGREEK MUSTARD over pork.
Heat vegetable oil in a large skillet over medium-high heat then fry pork until browned on all sides, about 15 minutes. Transfer pork to a large roasting pan. Add onion, carrots, celeriac and spring onion to the same skillet used to fry pork then cook and stir until vegetables are tender, about 10 minutes. Spread vegetable mixture around pork in roasting pan.
Pour ½ cup SIDS RASPBERRY VINEGAR into the skillet used to cook the pork and vegetables then simmer and scrape up any browned bits from the bottom with a spatula.
Pour over pork then bake in oven until pork is slightly pink in the center, 2½-3 hours, basting often. An instant-read thermometer inserted into the center should read at least 63oC. If vegetables become dry, add hot water as needed. Alternatively, cook everything in a slow cooker.
Transfer pork roast to a large platter and keep warm. Strain remaining liquid through a sieve into a saucepan and reserve vegetables.
Bring liquid to a boil and add butter and cornflour then simmer until sauce is thickened, about 5 minutes. Slice pork and serve with sauce and vegetables.