Salt and pepper, to taste
Untie roast, open and pound lightly to even thickness.
Cook celery and shallots (or onion) in butter until tender. Combine with ground pork, parsley, brandy and seasonings. Spread over roast. Lay a row of chestnuts down the center of stuffing. Chop remaining chestnuts finely and set aside. Roll meat around chestnuts and tie firmly. Roast in a 350° oven 1 1/2 hours or until meat thermometer reads 155-160°. Remove roast and let rest 10-15 minutes before carving.
Pour off extra fat; measure 2 tablespoons. Stir flour into 2 tablespoons fat. Add chicken broth, cook and stir until mixture thickens. Add reserved chopped chestnuts, parsley and brandy. Season to taste with salt and pepper. Serve gravy with roast.
Source: National Pork Board