Knuckles, leg bones with lots of marrow are the best for making soup. The marrow will also make the soup rich and thick. The bones are pre-boiled for a few minutes on high heat to clean the bones and get rid of the nasty scum.

* Step 2

Bring a big stockpot of water to a boil on high heat. Add the bones and boil hard for 10 minutes. You’ll see brownish scum rise to the surface. If you hadn’t taken the time to pre-boil the bones, all that scummy stuff ends up in your soup.

* Step 3

While the water is boiling in the step above, place the onion and ginger in the oven for 20 minutes on broil. Cook until the ginger is browned on both sides and the onion half is nicely browned and softened. Add the ginger and the onion to the slow cooker.

* Step 4

Next, saute the coriander seeds, fennel seeds, cardamom seeds, star anise, and cinnamon stick for 1-3 minutes until you smell a toasty aroma. Add all the spices to slow cooker

* Step 5

Fill the Crock Pot with fresh, clean, cool water to just 1-1/2 inches below rim, add the fish sauce and sugar. Cover and set the Crock Pot or slow cooker to cook on low for 8 hours. Taste and season with additional fish sauce if needed.

* Step 6

Strain the stock with a fine meshed sieve. Discard the solids. Take out the ox tail and beef shank. Remove the meat from the bones. Thinly slice the meat and return to the slow cooker.

* Step 7

When you are just about ready to eat, you'll prep the rest of the ingredients for the Pho bowls. Bring a pot of water to a boil. Add the beef balls and cook until heated through, about 2 minutes. Remove the balls, keeping the water boiling and now cook the noodles according to package instructions. If you are using fresh noodles, all they need is a couple of minutes. Drain immediately.

* Step 8

Put some noodles in a soup bowl. Add fish sauce, bean sprouts, cilantro, and green onions on top. Top it off with some of the beef chuck, beef shank, and ox tail meat you set aside earlier. Finally, ladle enough soup into the bowl so that it covers the noodles and toppings to your liking.