Korean slow-cooked beef soup with radish (moo tang)

This soup goes great with kimchi (store-bought, in the background).  Soak 5 pieces (about 3 lb) bone-in beef shank in water for about 10 minutes, then placed the drained beef into a large stock pot, covering with about 10 cups water.  Add 2 large onions, halved and peeled, and one head of garlic (peeled and separated into individual cloves). Bring to a boil, then let cook on a rolling simmer until beef is tender and soup smells fragrant (about 2 hours), skimming off scum to keep broth clear.  Top off broth if a significant amount evaporated (we usually add about 4 cups hot water). Remove bones and beef.  Discard bones and shred beef.  Return beef to pot, along with 1 large (2 lb) daikon radish, cut into thin (¼
inch) half-moons and/or wedges.  Add 3 bunches scallions, trimmed and cut into straws (about 3 pieces per scallion), then continue to cook until radish and scallions are tender.  Season generously with salt and a little black pepper. Serve with short-grain rice.  (Jan. 2015)

Note: You can use about 5-6 medium purple topped turnips in lieu of 2 lb daikon. If you do, cut the turnip thicker (about ½ inch thick) to avoid having the turnip disintegrate in the broth.