Beer and Rump Pot Roast

Name: Beer and Rump Pot Roast
Ingredients: 3 pounds rump roast, larded with strips of pork fat (ask a butcher to do this), patted dry; Freshly ground salt; Freshly ground black pepper; 2 tablespoons flour; 1/3 cup plus 2 tablespoons clarified butter; 1 medium onion, thinly sliced; 4 bacon slices, cut into 1/2-inch pieces; 1 tablespoon brown sugar; 16 ounces. water; 16 ounces bitter beer, flat; 2 tablespoons white wine vinegar; 1 bay leaf; 3 cloves; 1 lemon, juiced; pinch cayenne; 2 teaspoons arrowroot; 12 oysters, shucked; 1 cup mushrooms, thinly sliced