Despite the name, Sichuan peppercorns are not related to the more common black and white peppercorns, which grow on a vine. Sichuan peppercorns are small berries from the prickly ash shrub, and while they are used in other regional Chinese cuisines they are associated most strongly with the food of Sichuan province. The berries (called fa chiew in Cantonese) have a thin, delicate husk that splits open to reveal a tiny black seed. The peppercorn's small size belies its strong fragrance, but its most distinctive characteristic is its curiously numbing effect on the tongue - almost like Novocaine.
In Sichuan markets, you'll see piles of fa chiew for sale, ranging in colour from dull, pale brown to brick red, and at varying prices. The selection in Hong Kong is limited, so use your nose to decide if the peppercorns are worthy of purchase: if the fragrance is faint, they will have less flavour.
As with many other spices, the fragrance and flavour of Sichuan peppercorns become stronger when heated. Place the peppercorns in a dry, un-oiled wok and toast over a low heat, stirring constantly to prevent scorching, which imparts a bitter flavour. The fragrance and flavour fade with time so don't toast them too far in advance.
Sichuan peppercorns are used in five-spice powder and in the spicy, pepper-salt mixture sometimes served with Chinese roasted pork. To make pepper-salt, toast the Sichuan peppercorns until fragrant then cool and pound in a mortar or grind in a spice grinder. Sieve the ground peppercorns to remove large pieces of husk, then mix with sea salt and a little five-spice powder. Use instead of ordinary salt and pepper.
In Sichuanese cuisine, the peppercorns are often combined with another characteristic flavouring from the province: chillies. If you see a Sichuan soup listed on a hotpot menu, you can be sure Sichuan peppercorns and dried chillies will be floating in the broth, giving it a uniquely numbing and spicy flavour.
For an easy cold chicken dish, mix together ground, roasted Sichuan peppercorns with Sichuan chilli oil, soy sauce, sugar and sesame oil or sesame paste. Roast or poach a chicken then slice or shred into slivers. Toss the chicken with the chilli mixture and julienned spring onions and serve on blanched fun pei (mung-bean sheets) at room temperature. The chilli mixture is also good as a dipping sauce for thin slices of poached fatty pork.