Preheat broiler to high.
Place beef bones, onion, and ginger on foil lined baking sheet. Broil until everything has a nice char, about 8 minutes. Place beef, onion, and ginger in slow cooker.
Saute the cinnamon, coriander seeds, fennel seeds, star anise, cloves and cardamom pods in a dry skillet over medium high heat until toasted and frangrant. Place in a cheesecloth square and tie up. Add the spice package, the water, beef base, fish sauce, sugar and 1 teaspoon of salt in slow cooker. Cook on low for 8-10 hours.
When you are about ready to eat, cook the noodles per directions leaving them al dente. Drain and rinse with cold water and place in serving bowls. Remove bones and spices from broth and skim off any scum if necessary. Taste and adjust seasonings.
Place thin slices of beef and red onions slices on top of noodles. Ladle over the hot broth. Serve with condiments.