Place the oxtail in a large bowl, sprinkle over the flour and gently toss to coat. Heat the oil in a large heavy-bottomed pot over high heat. Add the oxtail in 2 or 3 batches and brown on all sides, about 5 minutes. Transfer to a plate.
Wipe the pot clean. Melt the butter over medium heat, and then saute the carrots, ginger, garlic, bell peppers, habanero and onions until starting to soften, 4 minutes. Add the browned oxtail with the stock, sherry, black bean paste, sugar, allspice, black pepper, tomatoes and star anise. Bring to a simmer and skim off any foam that rises to the top.
Simmer uncovered for 3 hours. If the liquid reduces too much, add a little water to keep the oxtail submerged in liquid. The oxtail meat should be falling off the bone and the liquid should be starting to thicken up a little.
Pour the black bean gravy over the oxtail and serve warm.