Place ginger and onions on a lightly oiled baking sheet. Brush some oil on the onion and ginger as well. Turn broiler on high and broil for 15 minutes. This will char them a bit and that's okay
Fill a big pot with water, enough to cover the bones, and boil the beef bones and oxtails for 15 minutes. Drain off the water and rinse the bones with cool running water. Refill the pot with bones and new fresh water to cover the bones and oxtails completely. Bring the water back to boil and skim off the scums as they appear. Add the charred ginger, onion, spice packet, sugar, fish sauce, salt and simmer uncovered for 4 hours
Strain the broth after 4 hours and discard all the stuff in there. I set aside the oxtails and pick the meat off the bones to serve with the pho later. Taste the broth and adjust with more salt, sugar or fish sauce if needed. At this point the broth is ready.
Cooking the noodles:
If using dried pho noodles, boil them for 3-5 minutes until they are cooked but still a bit chewy. If you are using fresh rice noodles, then it takes only 1-2 minutes to cook. Do not overcook them
Portion noodles and thinly sliced beef into individual serving bowl. Laddle the hot soup over and this will help to cook the beef. If you want it medium to fully cooked, you can submerge the beef slices into the soup briefly for few seconds until they turned brown. I like mine rare to medium rare :)
Serve with fresh bean sprouts, basil, saw tooth leaves, lime and peppers at a side. You can also eat it with Hoisin sauce and Sriracha chili sauce.
Pho Bo (Vietnamese Beef Pho Noodle Soup) https://whattocooktoday.com/vietnamese-pho-noodles.html