Cover the black-eyed peas with cold water and soak overnight. Drain the peas. Soak the shrimp in cold water for 30 minutes, and then drain off excess water.
Place the peas, shrimp and onion in a blender, along with the beaten egg and 1/4 cup of the cornmeal, and purée until smooth. Add salt if necessary (the dried shrimp may already be salty).
Combine the remaining 1/4 cup of cornmeal and the flour in a bowl. Form the pea mixture into small patties and dredge them in the cornmeal mixture. Pour the oil into a frying pan and heat over moderate heat. Test by dropping in a little of the pea mixture. If it bubbles immediately and rises to the surface, the oil is ready. Drop 4 to 6 patties into the hot oil and panfry until golden, shaking the pan constantly, turning the patties once, about 1 to 2 minutes.
Remove with a strainer or slotted spoon. Drain on paper towels. Continue to panfry patties in batches. Serve with Tomatillo Scallion Mayonnaise.Servings: 4 to 6