4 pounds oxtails, trimmed of fat and cut into 2-inch pieces
3/4 cup unbleached all-purpose flour
1/4 teaspoon salt, or to taste
1/8 teaspoon freshly-ground black pepper, or to taste
1/4 cup olive oil
3 cups homemade or canned beef broth
1 cup dry red wine
1 large green bell pepper, seeded, de-ribbed and chopped
1 medium yellow onion, peeled and minced
3 large cloves garlic, peeled and minced
3 tablespoons tomato paste
1/2 teaspoon dried thyme
1/2 teaspoon cayenne pepper
Few sprigs of parsley (for garnish)
Rinse oxtail pieces under cold running water and pat dry with paper towels. Mix together the flour and salt and pepper in a shallow dish. Dredge the oxtails in the seasoned flour. Heat the olive oil in a large pot over medium-high heat. Brown the oxtails in 3 batches in the oil, turning once, about 3 minutes per side. When they have browned, remove them to a large plate.
Return all the oxtails to the pot with the beef broth, wine, bell pepper, minced onions, garlic, tomato paste, thyme and cayenne pepper. Bring to a boil, then reduce the heat, cover and simmer, stirring occasionally, until the oxtails are very tender, about 3 hours. Skim off the fat with a ladle. Taste and correct seasonings.
Transfer oxtails with a slotted spoon to a large serving bowl and keep warm. Bring the sauce to a boil over medium-high heat and reduce it until it is thick, about 10 to 15 minutes. Pour the sauce over the oxtails, then garnish with parsley.
Serve at once with steamed white rice.