-
1
Roast onions and ginger directly on rack of a gas burner over high heat, turning with tongs, until blistered and blackened, 10 to 15 minutes. (Alternatively, broil onions and ginger on foil-lined rack of a broiler pan about 5 inches from heat, turning occasionally, until charred, 20 to 25 minutes for onions; 25 to 30 minutes for ginger.) Transfer to a bowl and cool. When cool enough to handle, rinse and rub under cold running water to remove any blackened pieces (some areas will remain browned).
-
2
While onions and ginger roast, cover shanks with 2 quarts cold water in a 6- to 8-quart pot. Bring to a boil, then drain in a large colander (discard cooking water) and rinse well with cold water. Clean pot.
-
3
Wrap star anise, cinnamon stick, cloves, and peppercorns in cheesecloth and tie into a bundle with kitchen string to make a spice bag, then add to cleaned pot along with 4 quarts water, shanks, onions, and ginger. Simmer, uncovered, skimming froth occasionally, 2 hours. Add remaining quart water and return to a boil, then reduce heat and simmer, skimming froth occasionally, until shanks are very tender, about 1 hour more.
-
4
Freeze steak until firm but not frozen solid, 30 to 45 minutes, then slice across the grain with a sharp thin knife into less than 1/8-inch-thick slices.
-
5
Soak rice noodles in cold water to cover until softened, about 30 minutes, then drain in cleaned large colander. Cook noodles in a 6-quart pot of boiling water, uncovered, stirring, 1 minute, then drain.
-
6
Transfer shanks with tongs to a cutting board. Clean pot. When shanks are cool enough to handle, remove meat from bones and cut into small pieces, discarding bones, fat, and sinew. Set aside 2 cups beef (reserve remainder for another use).
-
7
Pour broth through a fine-mesh sieve into a large heatproof bowl, discarding solids. Measure broth: If there is more than 3 quarts (12 cups), boil in cleaned pot until reduced; if there is less, add water. Let stand until fat rises to top, 1 to 2 minutes, then skim off fat if desired.
-
8
Combine broth and beef (2 cups) in cleaned 6- to 8-quart pot and bring to a boil, then add fish sauce and salt and return to a boil just before serving.
-
9
Divide noodles among 6 large deep bowls. Top noodles with uncooked sliced steak and ladle boiling-hot broth (with pieces of beef shanks) over steak and noodles. (Hot broth will cook steak.)
-
10
Serve soup with accompaniments.
