Bring water, soy sauce, rice wine, brown sugar, ginger, white parts of scallion, garlic, cilantro stems, orange tea, star anise, and red pepper flakes to a boil in a 5-6 quart pot, then reduce heat and simmer, uncovered, 10 min. Add short ribs and gently simmer, covered, turning occasionally, until meat is very tender but not falling apart, 2 1/4 to 2 1/2 hours. Let meat stand in cooking liquid, uncovered, 1 hour. (Can be made a day ahead up to this point and left overnight in the fridge, which makes the fat easier to skim and in my opinion also makes the beef tastier).

Transfer meat to a cutting board with tongs and discard bones and membranes, then cut meat across the grain into 1/2"-thick slices. Skim fat from cooking liquid. Strain through a cheese cloth into a 3-quart saucepan. Add chicken broth and meat and reheat soup over moderately low heat.

Meanwhile, cook noodles in a 6-8 quart pot of boiling water until tender, about 7 min. Drain noodles well in a colander and divide among 4 large soup bowls.

Ladle broth over noodles and top with meat, scallion greens, bean sprouts, pickled mustard greens, cilantro sprigs, and red chili (if using).