A photo like it (beef noodles in Lanzhou) · N509FZ (CC BY-SA 4.0) via Wikimedia Commons · source
Lanzhou's rule is one clear, two white, three red, four green: clear broth, white radish, red chili oil, green herbs. Hand-pulling takes practice; hand-cut noodles from the same dough work fine.
For the broth: 1.5 kg (3 lb) beef shank and bones, 1 piece ginger, 1 tbsp Sichuan pepper, 2 star anise, 1 tsp fennel seeds, 1 small cinnamon stick, 2 bay leaves, 1 dried chili, 1 tsp salt plus more to taste
300 g (10 oz) daikon, sliced thin
For the noodles: 500 g (4 cups) bread flour, 290 ml (1 1/4 cups) water, 1 tsp salt, 1/2 tsp baking soda (or 1 tsp penghui alkaline powder)
For the chili oil: 120 ml (1/2 cup) neutral oil, 4 tbsp chili flakes, 1 tsp sesame seeds
To serve: chopped cilantro and garlic chives or scallions
How to make it
Broth (3 1/2 hr): Soak the beef in cold water 1 hour to draw out blood. Cover with 4 liters (4 quarts) water, bring to a simmer, skim, add the ginger and the spices in a bag. Simmer 3 hours. Lift out the beef, cool and slice thin. Strain and season; add the daikon for the last 15 minutes.
Dough (1 hr rest): Mix flour, water, salt and soda into a stiff dough, knead 10 minutes until smooth, cover and rest 1 hour. Knead again briefly; it should stretch without tearing.
Pull or cut (15 min): Roll into a log, cut into 4, roll each into a rope and oil it. Pull by stretching, folding in half and twisting, 5 or 6 times; or roll out 3 mm thick and cut into strips.
Chili oil (5 min): Heat the oil until shimmering, pour it over the chili flakes and sesame, stir.
Build (3 min): Boil the noodles 2 to 3 minutes. Put in bowls, ladle over broth and daikon, add beef, a spoon of chili oil, cilantro and chives.
Tips
The alkali gives the noodles their bounce; don't skip it.
Order 'mao xi' (thin) or 'er xi' at a counter; at home, thicker is easier.