Rub pork with a mixture of black and cayenne pepper. In a roasting pan combine onions and celery. Stir in the tomato sauce, broth and lemon juice. Pour this mixture into a shallow 4-litre casserole or roasting pan.
Place pork roast on top of mixture and cover. Braise in a 350º oven for 30 minutes. Add remaining ingredients except parsley. Continue braising 1 hour or until vegetables and roast are tender and a meat thermometer inserted in roast registers 160º. Sprinkle with parsley. Serve with braised leeks.