In a shallow dish, arrange the oxtail. In a small bowl, mix some soy sauce, Worcestershire sauce, sugar, salt, garlic and herb spice, browning sauce, paprika, cayenne pepper, and black pepper.
Apply the soy sauce mixture evenly to the oxtail on both sides; remove any excess.
In a large, deep skillet, heat the vegetable oil over medium-high heat. Sear the oxtail in heated oil, about 3 minutes on each side; remove to a plate and put aside.
In the same skillet, sauté the celery, carrots, onion, and garlic until they are tender, which should take approximately 5 minutes. Bring the beef broth, thyme, rosemary, and bay leaf to a boil.
Blend in the oxtail together with its juices and butter. Simmer, covered, over low heat for three hours, or until the oxtail reaches fork tenderness.
Raise the heat to high while uncovered. Cook for around 5 minutes, stirring occasionally, until the sauce thickens and reduces.