This is the one I use, it takes some time but it is easy and forgiving and very yummy.
PHO BO (BEEF NOODLE SOUP)
8 oz beef sirloin
1 ¼ lb wide rice noodles, soaked in warm water for 20 minutes
1 onion, halved and thinly sliced
6-8 scallions cut into long thin pieces
2-3 chilies, seeded and finely chopped
½ cup bean sprouts
1 large bunch each mint and cilantro, chopped
2 limes cut into wedges
hoisin sauce and nouc cham sauces, to serve
For The Stock:
1 large oxtail or 1 lb beef short ribs, excess fat removed and cut into thick pieces
2 ¼ lb beef shank or brisket
2 large onions, peeled and quartered
2 carrots cut into pieces
3 inch piece of fresh ginger root, cut into chunks
2 cinnamon sticks
6 star anise
1 t black peppercorns
2 T soy sauce
4 T fish sauce
Place the oxtail in a pot and cover with water, bring to a boil and blanch for 10 minutes. Drain the oxtail, rinsing off any scum. Clean off the pan and put the oxtail back in with all the other stock ingredients except for the fish sauce. Cover the ingredients with about 12 litres of water. Bring to a boil, reduce the heat and simmer for 2-3 hours. Remove the lid and simmer for another hour until the stock is reduced to about 8 cups. If possible let the stock sit overnight. Skim off any fat and strain the stock into another pan. At this point the stock can be refrigerated or frozen for later use.
When ready to serve bring the stock to a boil, add the fish sauce and adjust the seasoning, reduce the heat to a simmer and keep very hot for serving.
Cut the beef sirloin across the grain into very thin pieces. Bring a pot of water to a boil and cook the rice sticks (noodles) until al dente. Divide the noodles, beef and other serving ingredient evenly among the bowls and ladle the hot stock over. Pass the lime wedges, fish sauce, hoisin and nouc cham at the table
I don't remember where I got it from, it lives in my recipe file on my computer.