If you are making the braised oxtail above, then it makes sense to cook a little extra and use the skinny tail pieces for a hearty soup. You can buy packets of mixed, quick-cooking, small, dried pulses from good supermarkets these days which is perfect for soups like this. Some don't even need soaking, so check the packet.
A good knob of butter
1 small onion, peeled, halved and finely chopped
A few sticks of celery from the recipe above, cut into rough cm dice
1 small carrot, trimmed, peeled and cut into rough cm dice
A couple of sprigs of thyme
60g small dried pulses, soaked for 2-3 hours in cold water
The remaining sauce from the oxtail plus extra beef stock to make it up to about 1.5ltrs
The remaining small ends of oxtail removed from the bone
Salt and freshly ground black pepper
Melt the butter in a heavy-based saucepan and gently cook the onion, celery, carrot and thyme for 2-3 minutes, without colouring, until it softens.
Add the remaining sauce and stock, bring to the boil, add the pulses and simmer very gently for about 30 minutes or until the pulses are tender. Add the pieces of oxtail, season and simmer for a couple of minutes, then serve.