To season the shrimp: In a bowl, combine the shrimp with salt and white pepper. Mix well and set aside.
To start the omelet: Heat a pan over medium heat and place the dry rice paper flat in the pan. Crack the egg in the center and spread it evenly over the rice paper. Add the seasoned shrimp and scallions on top.
To fold the omelet: Allow the egg and shrimp to begin cooking, then carefully fold the rice paper in half over the filling.
To crisp the omelet: Add the cooking oil around the folded omelet. Continue cooking over medium heat, carefully flipping as needed, until the shrimp is fully cooked and the rice paper is golden and crispy on both sides.
To make the dipping sauce: In a small pot over medium heat, combine 1 cup water, rice vinegar, ketchup, sugar, and salt. Bring to a simmer. Mix the cornstarch with 3 tablespoons water, then slowly stir the slurry into the sauce. Cook until thickened and remove from the heat.
To serve: Serve the Rice Paper Omelet whole or cut in half, with the sweet and sour dipping sauce on the side.