Brown the beef, then cook the onions:
Heat 2 teaspoons oil in a large, thick-bottomed pot on medium high heat. Add the shank slice or stew beef. Let the beef brown lightly on one side, then turn over.
Add the chopped onions to the pot. Let the onions cook and soften, about 5 minutes.
Add 4 cups broth and simmer until the beef is tender:
Pour 4 cups of the beef broth over the beef and onions in the pot. Bring to a boil. Lower the heat to a simmer. Cover and cook until the meat is falling-off-the-bone tender, about 1 hour and 30 minutes.
Meanwhile, prep and roast the root vegetables: