When the onion or shallot starts to smell good, bake them in the oven at 400°F for about 15 minutes. To avoid browning the broth, remove any burned parts and set aside.
(Optional) Blanch the pork bones to remove impurities: Pork bones should be added to a big stockpot along with water to cover by 1 inch. When you see a lot of froth at the top after 10 minutes of boiling the bones, stop. After emptying the pot's contents into a colander, pour cold water over the bones to clean them. This keeps the stock clear and aids in cleaning the bones. It also aids in eliminating any residual, repulsive pig odor.
Bring 3 liters of water to a boil in a stockpot (if you are reusing the same stockpot that was used to blanch the bones, make sure to clean the pot thoroughly before adding water for the stock). Include the boiled bones with the onions and shallots. Turn down the heat to the lowest level, cover the pot, and simmer for two hours. Take the onions and pork bones out of the soup and throw them away. When there is still a significant quantity of meat on the bones, I will occasionally leave them.
Spice up the stock. Add fish sauce, sugar, salt, and powdered mushroom or chicken bouillon. Add annatto oil to the broth to give it an optional red/orange tint.
As directed on the packaging, prepare the noodles. Add 1/2 teaspoon of sesame seed or vegetable oil and lightly stir the noodles together if they are sticking together.
Add a few noodles to a bowl and assemble. Add some fried fish cakes and Vietnamese ham slices. Pour in the hot broth. Add cilantro or scallions and some freshly ground black pepper as garnish.