Wash the pork neck and pat dry. Mix onion soup powder, cumin, cayenne pepper, paprika powder and ginger and rub the meat all around with it. Place the meat in an ovenproof dish or roaster, cover with cling film and chill overnight.
The next day remove the foil from the casserole dish. Place the meat on the fat pan of the oven and cook in the preheated oven (electric cooker: 150 °C/ convection oven: 125 °C/ gas: see manufacturer) for approx. 5 hours.
Top the roast in between with frying stock.
In the meantime, wash the chives, shake dry and cut into fine rolls. Mix butter with mustard and chives.
Take the finished roast out of the oven, cover with aluminium foil and let it rest for about 10 minutes. Use 2 forks to remove fibrous meat from the roast. Cut bread into slices, spread with mustard butter and spread meat on top.