Put the tomatoes on a sieve, drain and collect the juice. Cut the tomatoes into pieces and put them back into the tomato juice. Peel onions and cut them into slices. Clean and wash the celery and cut it into pieces of about 2 cm length.
Wash oxtail, dab dry. Heat the oil in a frying pan and fry the tail pieces thoroughly all around. Add onions, fry briefly and sprinkle with salt and pepper. Deglaze with 1/4 litre of water and pour on the tomatoes.
Add the celery stalks. Wash the sage and rosemary, dab dry and put something aside for garnishing. Remove the remaining rosemary needles and cut the sage leaves into fine strips. Add to the roaster, bring to the boil, cover and cook on the stove or in the oven for 2-3 hours.
Season with salt and pepper and arrange on a deep plate. Serve garnished with fresh herbs. Spätzle are delicious with it.