How to Make It
In a large enameled cast-iron casserole, heat 2 tablespoons of the vegetable oil. Season the oxtail pieces with salt and pepper and add half of them to the casserole. Cook over moderately high heat until the oxtails are browned all over, about 8 minutes. Transfer the browned meat to a bowl and repeat with the remaining oxtail pieces. Carefully pour off the fat from the casserole.
Add the remaining 1 tablespoon of oil to the casserole. Add the chopped ginger and garlic and cook over moderate heat, stirring a few times, until golden and fragrant, about 5 minutes. Stir in the sake and scrape up any browned bits from the bottom of the casserole. Add the beef stock and bring to a simmer. Return the oxtails to the casserole, cover and simmer over low heat until the meat is very tender, about 3 hours.
Transfer the oxtails to a large rimmed baking sheet and let cool slightly. Remove the meat from the bones and cut into bite-size pieces; discard the bones, fat and gristle. Strain the broth, pressing down on the solids. Skim off the fat.
Return the broth to the casserole. Add the sliced daikon and leek and bring to a boil. Cover the casserole and simmer over low heat until the daikon is tender, 45 minutes. Add the oxtail meat, season with salt and pepper and keep hot.
In a large pot of salted boiling water, cook the ramen, stirring often, until al dente, 5 minutes. Drain and return to the pot. Fill the pot with cold water and drain again. Rinse and drain the ramen one more time.
Transfer the ramen to large bowls and add the daikon and leek. Ladle the broth and oxtail meat into the bowls and serve, passing the 1/2 cup Golden Garlic Chips and chopped chives at the table.