There were days a couple of years ago when you might have spotted Lee Hefter, executive chef of Spago Beverly Hills (and formerly at Spago on Maui), prowling through shops in Chinatown searching for an ingredient that then was almost impossible to find — Sichuan peppercorns.

Hefter wanted the aromatic, camphor-scented spice because it imparts a unique, elusive fragrance and a mysterious flavor note to the Chinese-style dishes that he makes from time to time.

The problem was, Sichuan peppercorns had been banned in the United States. The ban was imposed because the tree from which they're harvested, a citrus-family tree whose name translates as prickly ash, carries pests that could infect U.S. orchards, according to the Animal and Plant Health Inspection Service of the U.S. Department of Agriculture.

Despite the ban, stray packages turned up on store shelves until two or three years ago, when suddenly they vanished, seemingly for good.

Hefter gathered what he could in Los Angeles' Chinatown and hunted in Chinatowns elsewhere. "I remember there was a period of time when we were without them," he says. What did he use instead when he couldn't get Sichuan pepper? He simply changed his recipes. The taste of Sichuan pepper is one of a kind. "You either have it, or you don't. You don't substitute for it," he says.

Now Hefter has all the Sichuan peppercorns he could possibly want.

About two years ago, it was found that heating the peppercorns to 140 degrees made them safe enough to import. Roasted before they enter the United States and accompanied by a document verifying the process, the peppercorns now are freely imported.

Ordinary peppercorns are Piper nigrum. The botanical name for Sichuan pepper is Zanthoxylum simulans. It is the fruit of a tree that grows in Sichuan province, China. The flavor is different if the tree is grown elsewhere, purists say.

Ask for Sichuan peppercorns in an Asian shop and you're likely to draw a blank stare. To find them, you may have to use the Chinese names: hua jiao (Mandarin) and faa jiu (Cantonese). The labeling on the package varies too. "Dried prickly ash," "dehydrated prickly ash" and "dried pepper" are some of the English names used. You can quickly recognize the peppercorns, though. They are tiny reddish shells, each containing a black seed.

Why all the fuss over what seems an obscure seasoning? Because the flavor is so unusual, with a delicate nuance of camphor and what Hefter characterizes as a "lemony overtone."

Assured of a regular supply, Hefter has been able to put dishes such as honey-lacquered squab on the menu. This sweet-spicy dish features Sichuan pepper-salt, which Hefter makes by grinding together four parts kosher salt to one part Sichuan peppercorns. Hefter learned about the roasted pepper-salt when working with the late Barbara Tropp at China Moon Cafe in San Francisco in the early '90s. He uses the blend when he wants to add complexity, especially to meat dishes.

Luis Diaz, executive chef of Chinois on Main in Santa Monica, Calif., uses the spice in a grilled New York steak dish. The steak is marinated in a ginger-garlic-hot chile mixture, then, while grilling, Diaz sprinkles the steak with Sichuan pepper. Although he calls the dish Sichuan beef, it's quite mild. "It's one of the classic dishes we have here," he says.

Chinese food authority and author Carl Chu says the combination of hot chilies and the haunting, sensual flavor of Sichuan pepper produces a "numbing" effect that is the "distinguishing mark of Sichuan cuisine."

"The flavor is so intoxicating, people get hooked on it," he says.

But not all authentic Sichuan dishes are fiery, and some featuring Sichuan pepper don't call for hot chilies. A cold chicken preparation adapted from Robert A. Delfs' "The Good Food of Szechwan" combines the ground aromatic peppercorns with that everyday Asian quartet of ginger, soy sauce, rice vinegar and sesame oil to make an enchant-ingly fragrant sauce that transmutes a simple poached chicken breast into a tantalizing and memorable delicacy.