How to Make It
Place shrimp on their sides on a cutting board. Holding shrimp by the tail and using a rolling pin or meat mallet, tap each shrimp lightly until slightly flattened (about 3/8 inch thick), 3 to 5 times.
Pour oil to a depth of 1/4 inch in a large cast-iron skillet, and heat over medium-high until hot but not smoking.
Meanwhile, whisk together flour, cornstarch, paprika, 1 teaspoon salt, and 1/2 teaspoon pepper in a shallow dish. Whisk together eggs in a large bowl until frothy; whisk in evaporated milk, parsley, remaining 1/2 teaspoon salt, and remaining 1/2 teaspoon pepper.
Working in batches, dip shrimp in egg mixture, allowing excess to drip off. Dredge in flour mixture; shake off excess. Add to hot oil, without crowding, and fry until golden and crisp, about 1 minute per side. (Adjust heat between batches to maintain temperature as needed.) Drain on a wire rack set inside a rimmed baking sheet; sprinkle with salt to taste.
Transfer shrimp to a large serving platter. Garnish with parsley, and serve with relish and lemon wedges for squeezing.