Place the beef bones on a roasting rack and bake in the oven at 350ºF for 30 minutes or in an air fryer for 20 minutes. Halfway through the cooking time, flip the bones over to roast the other side. If there's any bone marrow, scoop it out and enjoy it on a toasted baguette for a special treat!
Place the brisket in a large stock pot and cover with water. Bring to a boil and simmer for 10 minutes.
Carefully remove the meat and set it aside. Pour out the water and wash the pot. Give the brisket a rinse as well to remove all the impurities. This will give you a much clearer broth.
Return the brisket to the pot and add in the roasted beef bones. Cover with water and bring to a boil.
Remove the outer layer of the onion and cut it in half crosswise. Using tongs, lightly char the onion on all sides over a gas burner on medium/low heat. Do the same for the ginger slices. If you don't have a gas stove, you can skip this step. (See notes below.)
Using a frying pan over low heat, add the SPICES (cinnamon sticks, star anise, cardamom, coriander, cloves). Do not use any oil. We want to toast the spices to bring out the flavors. You'll start to smell the intense and fragrant aroma of the spices. At this point, everyone in the house will know you're making pho. Stir constantly until they begin to change color.
When the spices are toasted, add them to the stock pot along with the onion, ginger slices, fish sauce and salt.
Simmer over low heat until the meat is tender. For brisket it takes almost 3 hours. Remove the meat and allow it to cool before slicing.
Continue to simmer the bones for another 3 hours. Add more water as needed, just enough to cover the bones.
Using a fine mesh strainer, periodically skim the surface of the broth to remove impurities. We want to keep the broth clear.
When the final 3 hours are up, remove the bones from the broth. Using a strainer, fish out all the spices and remove any remaining impurities.
Skim off some of the fat floating on top of the broth. Leaving a little is OK, but the more you remove the better. You'll have a much lighter broth that won't weigh you down.
Add more salt and fish sauce to taste. Adjust accordingly depending on how much liquid you have left after simmering. The broth should taste a tad on the salty side. Once poured over noodles, the flavor gets slightly diluted.
If you're using dried pho noodles, cook according to the package instructions. If using fresh pho noodles, 10-15 seconds in boiling water is all it takes. Don't over cook it.
To assemble, add the cooked noodles in a bowl. Top with sliced brisket, sliced white onion, chopped cilantro and scallions. Ladle the hot broth over the top. Garnish with fresh bean sprouts, basil, fresh chilis and a squeeze of lime.
Notes
You can opt to char the halved onion and ginger slices over an open flame. I put the onion directly on the stove grates over medium/low heat until it begins to char on all sides. With tongs, I char the ginger slices one at a time over the open flame. This adds additional flavor and color to your broth. I mention this as optional because it can be a little dangerous if you don't watch it closely. Do this only if you feel 100% comfortable.