I have been browning them and then throwing in either red wine or tomato sauce and even Worcestershire sauce; and of course onions, or garlic, and anything from bay leaves to chocolate powder.
So far I like one of the first recipes that I used, although i didn't follow it closely. i added carrots to this recipe about 25 minutes before it was done simmering. it was delicious and has so much nutritional value, because you get the marrow and collagen that you dont get when you are on a diet of "prime cuts"
4-5 lbs oxtails
freshly ground black pepper
2 TB oilve oil
1/2 large onion, thinly sliced
6 cloves garlic, chopped
1 tsp dried thyme
1 cup red wine
4 cups beef or chicken broth
1 medium bay leaf
Season the oxtails with salt and pepper. In a large, deep pot such as a dutch oven, heat oil. Brown the oxtails in batches, making sure not to crowd the pan.
Once all the oxtails have been browned, saute the onion about 3 minutes, until softened. Add the garlic and thyme, saute 1 minute, then add red wine to deglaze the pan. Stirring constantly, scrape up any browned bits stuck to the pan while wine reduces by half. Return oxtails to pan, add stock and bay leaf. The stock should almost cover the oxtails. Add more or less, as needed. Bring to a boil, reduce to a simmer, and cover pan.
At this point you can walk away from your stove. Check in with your oxtails every once in awhile, making sure they are happily simmering away. After 1 1/2 hours of cooking, turn the oxtails over. Cover the pan again, and walk away. Cook for another 1 to 1 1/2 hours, until meat is very tender. Remove the oxtails from the pan, and if necessary reduce the liquid until slightly thickened. Season with salt and pepper to taste.
Recipe by http://blackgirlchefswhites.com/wordpress/