Season the flour with the paprika, salt and pepper in a bowl. Add the oxtail pieces and coat evenly. Heat the oil and butter (med-hi heat) in a large ovenproof cast-iron pot/casserole on the stove. Brown the meat well on all sides. Remove meat from the pot, then add the diced red onion, chopped carrots, chopped celery sticks and the garlic and fry for 3-4 mins. (med heat) until you see some caramelisation. Stir in the bouquet garni and tomato puree. Add the meat and juices back into the pot.