THE BROTH
2 onions, halved
4" nub of ginger, halved lengthwise
5-6 lbs of good beef bones, preferably leg and knuckle
1 lb of beef meat - chuck, brisket, rump, cut into large slices [optional]
3 thinly sliced carrots
1 bunch of greens (spinach, kale, etc...)
6 quarts of water
1 fennel bulb
1 cinnamon stick
1 tbl coriander seeds
5 whole star anise
1/4 cup use soy sauce
1 inch chunk of yellow rock sugar (about 1 oz) - or 1oz of regular sugar
1 1/2 tablespoons kosher salt (halve if using regular table salt) (this is to taste, the soy sauce will already have some salt in it, so add this last right before serving it if needed)

THE BOWLS
2 lbs rice noodles (dried or fresh), flat "chinese" style noodles, or spaghetti noodles
cooked beef from the broth
1/2 lb flank, london broil, sirloin or eye of round, sliced as thin as possible.
(get the grocer or the meat store to slice for you before you leave)
big handful of each: mint, cilantro, basil
2 limes, cut into wedges
2 big handfuls of bean sprouts
2-3 chili peppers, sliced, optional
Hoisin sauce, optional
Sriracha hot sauce, optional

Directions:

In a separate pot, parboil the bones: Fill large pot (12-qt capacity) with cool water. Boil water, and then add the bones, keeping the heat on high. Boil vigorously for 10 minutes. Drain, rinse the bones and rinse out the pot. Refill pot with bones and 6 qts of cool water. Bring to boil over high heat and lower to simmer. Using a ladle or a fine mesh strainer, remove any scum that rises to the top.

Put about a tablespoon of oil in the soup pot. Dice the onions, and the fennel bulb. Add this to this to the pot, and saute until both are slightly clear. Add the broth from above into the pot.

Boil broth: Add ginger, spices, beef, sugar, soy sauce, salt and simmer uncovered for 1 hours. Add the carrots and the greens, and simmer for another 30 minutes.
Remove the beef meat and set aside (you'll be eating this meat later in the bowls) Continue simmering for another 1 1/2 hours. Remove the bones from the pot. Taste broth and adjust seasoning - this is a crucial step. If the broth's flavor doesn't quite shine yet, add one at a time, and taste: 2 teaspoons more of fish sauce, large pinch of salt and a small nugget of rock sugar (or 1 teaspoon of regular sugar). Keep doing this until the broth tastes perfect.

Prepare noodles and meat: Slice your flank/london broil/sirloin as thin as possible - try freezing for 15 minutes prior to slicing to make it easier. (Or get your local meat counter to slice it for you before you leave the store). Remember the cooked beef meat that was part of your broth? Cut or shred the meat and set aside. Arrange all other ingredients on a platter for the table. Your guests will "assemble" their own bowls. Follow the directions on your package of noodles - there are many different sizes and widths of rice noodles, so make sure you read the directions. For some fresh rice noodles, just a quick 5 second blanch in hot water is all that's needed. Make sure they're fully cooked separately before you assemble the soup.

Ladling: Bring your broth back to a boil. Line up your soup bowls next to the stove. Fill each bowl with rice noodles, shredded cooked beef and raw meat slices. As soon as the broth comes back to a boil, ladle into each bowl. the hot broth will cook your raw beef slices. Serve immediately. Guests can garnish their own bowls as they wish.

I adapted the recipe from here, it has a slightly more detailed explanation: http://steamykitchen.com/271-vietnamese-beef-noodle-soup-pho.html. I like my soups to have a little color, that's why i added the kale and carrots. Most restaurants won't have them in it.