Start to finish: 1 hour
1½ pounds shell-on medium-large shrimp
2 tablespoons Chinese rice wine or dry sherry
2 1/2 teaspoons black peppercorns, coarsely ground
2 teaspoons Sichuan peppercorns, coarsely ground
2 teaspoons sugar
¼ teaspoon cayenne pepper
4 cups vegetable oil
5 tablespoons cornstarch
2 jalapeno chiles, stemmed, seeded, and sliced into 1/8 inch-thick rings
3 garlic cloves, minced
1 tablespoon grated fresh ginger
2 scallions, sliced thin on bias
Adjust oven rack to upper-middle position and heat oven to 225 F. Set wire rack in rimmed baking sheet and line large plate with triple layer of paper towels. Toss shrimp with rice wine and 1 teaspoon salt in bowl and let sit at room temperature for 15 minutes. Combine black peppercorns, Sichuan peppercorns, sugar and cayenne in bowl.
Heat oil in large Dutch oven over medium heat until oil registers 385 F. Meanwhile, drain shrimp and pat dry with paper towels. Transfer shrimp to now-empty bowl, add 3 tablespoons cornstarch and 1 tablespoon peppercorn mixture, and toss until well coated.
Add one-third of shrimp to hot oil and fry, stirring occasionally to keep shrimp from sticking together, until light brown, 2 to 3 minutes. Maintain oil temperature between 375 F and 385 F. Transfer shrimp to prepared rack and keep warm in oven. Return oil to 385 F and repeat frying shrimp in 2 more batches, re-tossing each batch thoroughly with coating mixture before frying.
Return oil to 385 F. Toss jalapeno rings with remaining 2 tablespoons cornstarch in separate bowl. Shake off excess cornstarch, then carefully add jalapeno rings to oil and fry until crisp, 1 to 2 minutes. Transfer jalapeno rings to prepared plate. After frying, reserve 2 tablespoons frying oil.
Heat reserved oil in 12 inch skillet over medium-high heat until shimmering. Add garlic, ginger, and remaining peppercorn mixture and cook, stirring occasionally, until mixture is fragrant and just beginning to brown, about 45 seconds. Add shrimp, scallions, and ½ teaspoon salt and toss to coat. Serve immediately.