Preheat the oven to warm 170°C (Gas Mark 3, 325 °F). Coat the oxtail pieces in the seasoned flour, shaking off any excess.

Heat half the oil in a large frying-pan. Add the oxtail pieces and fry until they are evenly browned.

Transfer the pieces to a large flameproof casserole. Wipe the pan clean and pour in the rest of the oil. Add the onion and garlic and fry until the onion is soft.

Pour over the wine and bring to the boil, stirring constantly. Boil until the liquid has reduced by about half.

Pour the stock into the pan and cook for 2 minutes. Pour the mixture over the oxtail.

Stir the tomatoes, tomato puree (paste) and bouquets garnis into the casserole and bring to the boil. Cover and transfer to the oven. Braise for 3 1/2 hours.

Just before the end of the cooking period, blanch the celery pieces in boiling water for 5 minutes. Drain and stir into the casserole. Re-cover and braise for a further 30 minutes.

Remove from the oven and skim the scum from the surface. Set over moderate heat and stir in the cornflour (cornstarch) mixture. Bring to the boil and cook, stirring constantly, for 2 minutes, or until the liquid thickens and is smooth.