WHEN Asian food has a distinctive sourness that seems like citrus but is somehow more complex, chances are good that its flavor base is tamarind. The large seed pod of the tamarind tree is used in the cuisine of almost every equatorial country. Its pulp is processed into a dark brown paste, which is used as you might use tomato paste, concentrated stock or even ketchup: as a simple flavor enhancer that completely changes the nature of the sauce into which it is stirred.

Until recently, the only way to create tamarind paste was to buy a dark, sticky block of tamarind pulp. This mess, which could yield terrific flavor, had to be heated with water and strained before it could be put to any good use.

Far more convenient is pre-extracted paste, which is now sold in bottles in many stores specializing in Asian ingredients. (There is also a kind of instant tamarind powder, which is not very good.) It's concentrated to increase its strength, and some varieties have had citric acid added to emphasize their sourness; try to find a bottle that does not. (If you are stuck with paste that contains citric acid, omit the lime juice from the recipe below.) A quarter cup or so will turn a batch of otherwise ordinary shrimp into something exotic.

You can use this same process to make almost anything in a tamarind sauce, but shrimp, because it has minimal cooking time, is by far the easiest. I like to brown the shrimp first, but it isn't entirely necessary . When you stir in the paste, the sauce will turn deep brown. Due to the differences in intensity among pastes, it's important to taste at that point and add more tamarind if you think it's necessary. The dish is best when quite sour, rather than the sticky combination of sweet and sour that so many restaurants serve.


Time: 20 minutes

2 pounds shrimp, peeled and deveined

4 tablespoons butter

1 medium onion

2 tablespoons peeled and minced ginger

1 small fresh chili, stemmed, seeded and diced, or 1 teaspoon dried chili flakes, or to taste

1/4 cup tamarind paste, or to taste

1/4 cup fresh lime juice, or to taste

Salt and pepper to taste

Chopped cilantro leaves for garnish

Lime wedges.

1. Turn the heat under a large nonstick skillet to high, and heat for one minute. Add as many shrimp as will fit comfortably in one layer -- do not try to brown all at once. As soon as they begin to brown, about a minute later, turn them, cook about 30 seconds on the other side and remove from pan. Repeat until all shrimp are done, then turn off heat for a minute.

2. Turn heat to medium, and add butter; when it melts, add onion, turn heat to medium high and cook, stirring occasionally, until onion softens, about 5 minutes. Add ginger and chili, and cook for 30 seconds, then add tamarind paste and 1/4 cup water. Stir to blend, then taste, and add more tamarind paste if necessary; return shrimp to pan. Bring to a boil, then stir in lime juice; cook, stirring occasionally, until mixture thickens, a minute or so.

3. Taste and adjust seasoning, then garnish, and serve over rice, with lime wedges.

Yield: 4 servings.