1 oxtail, approximately 2 pounds, cut into pieces1 stalk of celery1 leek, white part only, sliced into strips2 carrots, cut into pieces1 onion, chopped3.5 tablespoons of butter (about 50g)4.5 tablespoons of all-purpose flour (about 60g)3/4 cup (180 ml) Madeira wine1 teaspoon Worcestershire sauceSalt, to tasteBlack pepper, to taste