Liberally salt and pepper the beef knuckles and place in a large stock pot (9 quart or larger). Cover with water and bring to a boil. Reduce temperature to and continue to cook for 2 hours.
Skim the fat from the surface and add the radish and onions. Place the star-anise pods, cinnamon stick, ginger and peppercorns on a piece of cheesecloth or the tea ball and tie into a pouch using butcher’s twine. Add to the broth mixture. Stir in sugar, salt and fish sauce. Simmer over medium-low heat for at least 4 more hours (the longer, the better). Salt as needed. Strain broth (discarding the spice pouch and bones), and return to the pot to keep at a simmer.
Bring a large pot of lightly salted water to a boil. Soak the rice noodles in water for about 20 minutes, then cook in boiling water until soft (about 5 minutes). Slice the frozen beef paper thin. The meat must be thin enough to cook instantly.
Return broth to a boil. Place some noodles into each bowl, and top with a few raw beef slices. Ladle boiling broth over the beef and noodles in the bowl. Serve with hoisin sauce and sriracha sauce on the side. Set onion, cilantro, bean sprouts, basil, green onions, and lime out at the table for individuals to add toppings to their liking