1 ½ pounds medium/large (31 to 40 per pound) shrimp, peeled, deveined, and tails discarded
3 quarts peanut or vegetable oil, for frying
1 teaspoon grated lemon zest
1 garlic clove, minced
1 ½ tablespoons Old Bay seasoning
1 ½ cups all-purpose flour
½ cup cornstarch
2 teaspoons pepper
1 teaspoon baking powder
1 ½ cups bottled clam juice
Toss shrimp, 1 tablespoon oil, lemon zest, garlic, and ½ teaspoon Old Bay in large bowl. Refrigerate, covered, for at least 30 minutes or up to 1 hour.
Adjust oven rack to middle position and heat oven to 200 degrees. Heat remaining oil in large Dutch oven over medium-high heat to 375 degrees. Combine flour, cornstarch, remaining Old Bay, pepper, and baking powder in large bowl. Stir clam juice into flour mixture until smooth. Fold marinated shrimp into batter until evenly coated.
Working quickly, add quarter of shrimp, 1 at a time, to oil. Fry, stirring frequently, until golden brown, about 2 minutes. Drain on paper towel-lined plate, then transfer shrimp to wire rack set inside rimmed baking sheet. Place shrimp in oven. Bring oil back to 375 degrees and repeat with remaining shrimp. Serve.