Combine chili oil with flakes, soy sauce, vinegar, sesame paste, sugar, Sichuan pepper, chicken broth, yacai and scallions and add to a serving bowl or divide among 3 to 4 individual-serving bowls.
While bringing water to a boil in a large pot, heat a dry wok until very hot and add lard (or oil). When lard is hot, add the pork and stir-fry, breaking up into very small bits, until it loses its pinkness. Add the wine, sweet wheat paste and salt and continue to stir-fry until the pork is lightly crisp. Drain the pork and keep in reserve.
Add bok choy to boiling water and cook 1 to 2 minutes, or until done; remove and hold. Add noodles to same pot and cook until just done. Reserve ¼ cup of the noodle water.
Drain noodles, leaving them slightly wet, and immediately layer into the bowl(s) on top of the sauce. Top the noodles with the pork and bok choy. At table, mix the noodles in with the sauce, distributing ingredients throughout. If the noodles are too dry, mix in a bit of the reserved noodle water. Alternatively, pre-mix the noodles in the sauce, then portion between bowls and top with pork and bok choy.