Step 1

Grate 1 teaspoon zest from lemon, then cut in half. Place both halves and 4 cups water in a saucepan; bring to a boil and add 1 tablespoon salt. Add shrimp; return to a boil, then reduce heat and simmer until just cooked through, about 1 minute. Drain; let cool 15 minutes. Peel and cut into a 1/4-inch dice (about 1 1/2 cups).

Step 2

Heat 1 1/2 inches oil in a medium heavy-bottomed pot over medium until a deep-fry thermometer reads 350°F. Whisk together flour, baking powder, sugar, 1 teaspoon salt, and lemon zest. Whisk seltzer and egg into dry ingredients. (Batter should have the consistency of thick honey. If too thick, add more seltzer; if too thin, add 1 tablespoon rice flour.) Stir in shrimp.

Step 3

Working in batches, and using two tablespoons (one to scoop, one to scrape), drop batter in oil. Fry, turning occasionally, until cooked through and golden brown, 3 to 4 minutes, adjusting heat as needed to keep oil between 340° and 350°. Transfer to a paper-towel-lined baking sheet; sprinkle with salt. Serve immediately with tartar sauce and lemon wedges and zest.