Char the onion and ginger under the broiler for about 10 minutes.

In a large pot, add the beef bones and cover with water. Bring to a boil for about 10 minutes, then drain and rinse the bones.

Return the bones to the pot and add 8 cups of fresh water, charred onion, ginger, star anise, cloves, cinnamon stick, fish sauce, and sugar.

Bring the pot to a gentle boil, then reduce the heat and let it simmer for 2-3 hours.

Strain the broth through a fine-mesh strainer or cheesecloth.

While the broth is straining, cook the rice noodles according to package instructions.

In each serving bowl, place a portion of noodles and thinly slice the brisket, arranging it over the noodles.

Pour the hot broth over the noodles and beef, then garnish with fresh herbs, lime wedges, jalapeños, and bean sprouts.