I make a stew which to be honest, is similar to the soup.
First i brown the chopped oxtails in large heavy based casserole pan along with a little crushed garlic or garlic paste, some tomato paste and olive oil.
When lightly brown, remove oxtail onto plate, add chopped red onion, chopped carrot, more garlic in whole cloves, salt, thyme and slowly panfry until lightly browned. I then place the carrots, onions, garlic onto plate with meat.
I add a little cornflour to the pan juices and scrape and stir until flour is smoothly mixed in. I then add a little more cornflour paste and a little more stock. Stir, then pour in another 200ml of half stock/half red wine and stir. Bring to simmer and keep stirring then add meat and veg. The liquid should just cover the meat mix. Add more wine if necessary.
Place in oven on low heat 180 and cook for 2 hours. Check then and see if meat is falling off of the bone which means it's done.
Make sure you check the liquid levels every twenty mins. Add more if necessary and if its getting too thin, stir in a tiny bit more cornflour/water paste.
The beauty of oxtail is that the marrow and gelatine from the bones make an unctuous dark sauce and one which improves if you cook it one day, keep in fridge overnight then reheat the next day.
Best to add the cornflour as a paste as added neat tends to make it clump/lumpy. I mix a little stock and cornflour on a plate into a paste. By adding a little butter as well you have a beurre Manie which can be beaten into the sauce to make it richer and thicker.
It's really a simple process-you can always just brown the oxtails then chuck it all into a pot also.