In a large pot, combine the beef shank, beef brisket, beef broth, water, onion, garlic, and ginger. Bring to a boil over medium-high heat, then reduce to low and simmer for about 1.5 to 2 hours, or until the beef is tender. Skim off any foam that rises to the surface.

Once the beef is tender, remove it from the pot and set aside. Strain the broth to remove the solids, then return the broth to the pot.

Stir in the fish sauce, chili paste, sugar, salt, and black pepper. Adjust the seasoning to taste.

While the broth is simmering, cook the rice vermicelli noodles according to package instructions. Drain and set aside.

Slice the cooked beef into thin pieces.

To serve, place a portion of the noodles in a bowl, top with sliced beef, and ladle the hot broth over the top.

Garnish with bean sprouts, cilantro, lime wedges, and jalapeños if desired. Finish with sliced green onions.