Halve onions lengthwise and slice ginger into thick coins.

Cook onions and ginger in a stockpot with peanut oil over medium heat until onions begin to color.

Rinse beef shanks and cover with cold water, bring to a boil, then discard the water and re-rinse.

Add shanks to the stockpot with 6-7 quarts of water.

Toast star anise, cinnamon sticks, cardamom pods, black peppercorns, and cloves in a skillet until fragrant, being careful not to burn them.

Add the toasted spices to the stockpot and bring to a gentle boil, then simmer for 4-6 hours, partly covered, adding water as needed.

Add the brisket to the soup 2 hours before the end of the cooking time.

Place sirloin in the freezer for 30 minutes to firm it up.

Slice the sirloin against the grain as thinly as possible and refrigerate.

Strain the stock through a colander, check seasoning, and add salt or fish sauce to taste.

Salvage any meat from the soup bones and slice the brisket thinly, then refrigerate.

Cool the stock and remove the hardened beef fat from the top.

Reheat the stock.

Soak or cook the rice noodles according to package directions, slightly undercooking them.

Blanch the bean sprouts for 30 seconds in boiling water and drain.

Place noodles in individual bowls and layer with brisket and sirloin.

Pour hot broth over the bowls to cook the sirloin.

Serve with basil, limes, sprouts, Vietnamese chili paste (sriracha), and fish sauce for seasoning.

Stir well to combine the ingredients before eating