The fathers in my life have always been absent on Friday nights. My real father was a fiend for poker, and Po-fu, my adopted Chinese father, was addicted to a weekly shot of mah-jongg. The one advantage of their absence was an evening of special eating. In my American childhood I wolfed down enough potato chips and pretzels to last the week, secretly and under the covers. In Taiwan, I scampered off in full view and with full approval to enlist “take out” at our neighborhood Moslem restaurant. My order was always the same—a half-gallon of hot and sour soup and enough pot stickers for the household. Never, not once, was it less than the-best-soup-I-have-ever-eaten.
In separate bowls, soak the tree ears and lily buds in cool or warm water to cover until supple, about 20 minutes. Cover tree ears generously, with about 2 cups water, to allow for expansion. In a third bowl, cover the mushrooms with cold or hot water and soak until soft and spongy, 20 minutes to an hour. All three items may be left to soak overnight with no loss of flavor.
Drain the tree ears, swish well in an ample amount of cool water to dislodge grit, then drain and repeat. Pick over and discard any unchewable or overly gelatinous bits, then tear the tree ears if needed into quarter- or nickel-size pieces.
Drain the lily buds and snip off the hard stem ends. Cut them in half crosswise.
Drain the mushrooms, snip off the stems, then rinse to dislodge any sand trapped in the gills. Cut the caps into thin slivers ⅛ inch wide. Combine with the drained tree ears and lily buds.
Cut the beef crosswise against the grain into slices a scant ¼ inch wide, then cut lengthwise against the grain into long shreds a scant ¼ inch thick. Cut the shreds crosswise into 1½–2-inch lengths. (Partially freezing the meat before shredding is not necessary here, as it usually is in a stir-fry. The liquid medium of a soup is not as demanding of even slices, and the slight irregularity of the slivers is charming in a soup.)
Mix the marinade ingredients until smooth, then toss well with the beef. Marinate for 30 minutes at room temperature or overnight in the refrigerator, sealed airtight. Stir once with your fingers midway through the marinating to redistribute the seasonings. Bring to room temperature before cooking.
Holding a sharp knife parallel to the board, cut the tofu through the middle into slabs ¼ inch thick, then stack the slabs and shred them into slivers ¼ inch wide. Cut carefully, so the tofu does not break. Refrigerate several hours or overnight if desired, covered with cool water. Drain before using.
About 10–15 minues before serving, combine the soy with the cornstarch mixture and leave the spoon in the bowl. Combine the vinegar and the pepper, and stir the meat to loosen the slivers. Have all the ingredients within easy reach of your stovetop. Put the soup bowls in a low oven to warm.
Bring the stock to a steaming near-simmer over medium heat in a 4–5-quart nonaluminum pot. Add the tree ears, lily buds, and black mushrooms, then slip the tofu gently into the pot. Swish once or twice gently to mix, cover, then cook until the stock boils. Add the beef, swish gently several times to mix, then reduce the heat to maintain a low simmer. Cover the pot and simmer 2 minutes.
Remove the cover, stir the cornstarch mixture to recombine, then pour it evenly into the soup. Stir gently until the liquid becomes glossy and slightly thick, 15–20 seconds. Add the vinegar and pepper, stir gently to blend, then turn off the heat.
Immediately add the egg to the soup in a thin stream, stirring gently as you pour it so it comes to the surface in chiffony wisps. Taste, and adjust with more vinegar and pepper, if desired. The taste should be vibrant and sharp—very hot and very sour. Work quickly, so the vinegar bite does not dissipate.
Stir in the sesame oil, then portion the soup into the heated bowls and garnish each with a thick sprinkling of scallion. Serve immediately.
The soup will keep nicely in the refrigerator for several days and can be frozen with great success. If necessary, respark with a bit more vinegar after reheating.
© 1982 Barbara Tropp estate. All rights reserved.