Making the oxtail: Sprinkle the oxtail generously with salt and pepper. In 2 batches, brown the oxtail on both sides in a saute pan over medium-high heat in 2 tablespoons of the olive oil. Set browned oxtail aside.
Making the curry: Deglaze the pan with the stout. Scrape any brown bits, along with un-evaporated stout, from the saute pan to a Dutch oven. Add the remaining tablespoon of olive oil to the saute pan and cook the onions over medium-high heat until browned, about 7 minutes. Add the garlic and chile, and cook for 1 minute. Add the curry powder and cook for 1 minute while stirring. Add the tomato paste and flour, and cook for another minute while stirring. Add the coconut milk and stir to blend. Transfer the sauce to the Dutch oven, add the beef broth and oxtail. Simmer, partially covered, over low heat until the oxtail is tender and starting to fall off the bone, about 3 hours. Add the yams and carrots and simmer for 35 minutes more. Skim off as much oil as possible. Season the curry with salt and pepper, and add the lime juice.
Serve with rice and lime wedges. Garnish with green onions.