1. Prepare the Batter In a large bowl, whisk together all dry batter ingredients. Add about ⅔ of the cold water and mix until a thick paste forms. Slowly add the remaining water, whisking until the batter is smooth and lump-free.
2. Prep the Fish Pat the fish dry thoroughly. Lightly coat each piece in flour, shaking off any excess.
3. Fry Heat oil to 350°F (175°C). Dip the floured fish into the batter, allowing excess to drip off, then carefully lower into the hot oil. Fry for 5–6 minutes, or until deeply golden and crisp. Drain on a rack.
4. Make the Sauce by mixing all tartar sauce ingredients into a small bowl.
5. Serve Serve immediately with tartar sauce and enjoy while hot and crunchy.