Oxtails are an odd cut of meat. They are tough and stringy, and the meat runs in narrow ropes along large chunks of bone. Yet, when cut into pieces and slow-cooked, oxtail becomes exceptionally tender and flavorful. Crock pot slow cookers provide a convenient method for preparing oxtail, requiring only a few minutes of preparation.
Place the oxtails on a cutting board and trim any excess fat with a sharp knife. If there are any blood spots or bone fragments, wipe them away with a damp paper towel. Plug in the slow cooker, and preheat it on its high setting.
Heat a heavy skillet on the stovetop to a medium-high temperature. Oil it lightly with vegetable oil or pan spray. Working in small batches, sear the pieces of oxtail until they are well browned on all sides.
Remove the oxtails to the crock pot, as they finish browning. If you are using the onion, carrot and celery, add them to the skillet and cook them in the beef drippings until they are slightly browned. Add them to the slower cooker.
Drain the fat from the hot skillet, and pour in a half-cup of water, red wine or beef broth. Scrape and stir vigorously with a wooden spoon until all the flavorful browned juices are softened and dissolved. Pour the liquid into the slow cooker.
Add another cup of beef broth or red wine to the crock pot, if desired, along with the bay leaf and salt and pepper. Cook on high until the liquids are steaming and there is a distinct aroma of beef, approximately 45 minutes.
Reduce the slow cooker to its low setting, and cook for four to six hours until the oxtails are fork-tender. Serve hot. The cooking liquid can be strained and boiled hard until it is thick enough to coat the back of a spoon, then served as a sauce over the meat.