Based on an idea from the St. Vincent's Rocks, Clifton, England
Stir in brown sugar. Add the water, beer (reserving 3 tablespoons), wine vinegar, bay leaf, and cloves. The liquid should cover the meat half way. Cover and simmer for 2 1/2 hours. Skim the fat from the surface and remove the cooked meat to a carving board.
Strain the meat braising liquid and return to roasting pan, skimming any remaining fat. Bring to a boil. Mix arrowroot with reserved beer and add to pan. Cook for another minute to thicken. Add the oysters and mushrooms.