Combine chopped pork with chicken livers and sliced veal, and mix together with marinade. Cover and refrigerate for 2 days. Saute shallots in butter. Add brandy and reduce by half.
Remove parsley sprigs and add marinade and marinated meats to a food processor along with the shallot mixture. Puree. Add diced fat, thyme and lightly beaten egg and pulse to mix. Line terrine with strips of fatback. Add pate mixture and cover it with the fat flaps. Put bay leaf pattern on top of fat and cover with aluminum foil, close the terrine lid and seal with flour and water paste. Preheat oven to 175 degrees. Place terrine in Bain-Marie. Fill with hot water (2/3 up the sides of roasting pan). Bake for 2 to 3 hours, or until instant read thermometer registers 165 degrees.
Remove terrine from Bain-Marie, remove lid and weight down the pate, and bring to room temperature. Chill in refrigerator overnight, still weighted. Serve at room temperature.