From Fuchsia Dunlop's wonderful Land of Plenty, although lightly adapted and modified, mostly for practicality: the sauce and the spinach are now combined in a single serving bowl, rather than arranged in each individual bowl. Also, for timid palates, the chili oil is now added at the table, rather than mixed in the general sauce. A few other notes: 1) There's no reason why you couldn't use frozen spinach here. 2) Lately I've been adding, wholly inauthentically, other vegetables to the serving bowl along with the spinach: some stir-fried thin-sliced red pepper, say, or stir-fried mushrooms. 3) The Tianjin preserved vegetables are optional but delicious and keep forever: they're sold in small crocks in any Chinese grocery store. —Nicholas Day
Toast the walnuts and peanuts, either in the oven (20 minutes at 250 degrees, on a baking sheet) or in a wok or saucepan (medium heat, 5 minutes or so, stirring frequently). Chop into small pieces. Then toast the sesame seeds: in a wok or sauce pan, cook the seeds over low heat for three or four minutes, stirring frequently. Put the seeds and the nuts in separate small bowls.
If you are using the preserved vegetable: heat a tablespoon of peanut oil in your wok or saucepan, then add the vegetable and stir-fry for a half-minute or so. Put the vegetable in a small bowl too.
Put a pot of water on to boil. Finely slice the scallions, using the green parts only, and place in another small bowl. Combine the sesame oil, the soy sauces and a couple tablespoons of peanut oil in a large serving bowl.
When your water is boiling, blanch the spinach, removing with a wire sieve (so the boiling water stays behind), and then cool under cold water. (You can also simply stir-fry the spinach until it wilts.) Drain well and chop very roughly. Then add to the serving bowl.
Cook the noodles according to directions. Drain and then add to the serving bowl. Toss well and serve. At the table, allow each person to top their bowl according to whim: there should be bowls of nuts, seeds, scallions, and preserved vegetable, plus a container of chili oil.