How to Make It
In a medium bowl, cover the salt cod with 3 inches of cold water and soak in the refrigerator for 2 days, changing the water at least 3 times each day.
Drain the salt cod, transfer to a medium saucepan and add enough cold water to cover the fish by 2 inches. Bring to a boil. Reduce the heat to low and simmer the fish until it just flakes with a fork, about 20 minutes. Using a slotted spoon, transfer the fish to a plate and let cool. Flake the fish and discard any bones or bits of skin.
Meanwhile, in a small saucepan, melt the butter. Add the onion, bell peppers and black pepper and cook over moderate heat, stirring, until the vegetables are softened, about 10 minutes. Scrape the vegetables into a small bowl and let cool.
In a large bowl, whisk the flour with the cornstarch, salt, sugar and baking powder. Mix in the egg and sparkling water with a fork until almost combined. Stir the flaked salt cod and the cooked vegetables into the batter.
In a large saucepan, heat 2 inches of oil to 350°. Carefully scoop eight 1-tablespoon balls of batter into the hot oil and fry, turning occasionally, until richly browned, about 4 minutes. Using a slotted spoon, transfer the fritters to a paper towel–lined plate to drain and season with salt. Repeat with the remaining batter. Serve the fritters hot with Curry Aioli and lime wedges.