Step 1

In a small heatproof bowl, use a fork to break up and stir the tamarind pulp into the boiling water. Let stand for 20 to 30 minutes. Strain through a fine-mesh sieve over a liquid measuring cup; press on the solids and scrape the underside to collect the pulp that clings (you should have about ½ cup strained pulp).

Step 2

To the tamarind, add enough room-temperature water to equal ⅔ cup, then whisk in the soy sauce, sugar, ¾ teaspoon salt and ¼ teaspoon white pepper. In a medium bowl, toss the shrimp with 2 tablespoons of the mixture; let stand 10 minutes.

Step 3

In a 12- to 14-inch wok or a 12-inch skillet over medium-high, heat 1 tablespoon of the oil until barely smoking. Add half of the shrimp in an even layer; cook without stirring until charred, 1 to 1½ minutes. Transfer to a plate. Return the pan to medium-high and, using the remaining 1 tablespoon oil, sear the remaining shrimp in the same way.

Step 4

Return the first batch of shrimp and any juices to the pan. If using a wok, pour the tamarind mixture down the sides of the wok; it should bubble vigorously. If using a skillet, simply add to the shrimp, then reduce the heat to medium. Cook, stirring, until the shrimp are opaque throughout and the sauce clings lightly to them, 2 to 3 minutes. Off heat, stir in the chili. Taste and season with salt and white pepper. Transfer to a platter; garnish with the cucumber and cilantro. Serve with lime wedges.