1. In a medium bowl, combine the mayonnaise, mustard, scallion, lemon juice, gherkins, capers, parsley, and a pinch each of salt and pepper. Heat the oven to 200°. Cover a baking sheet with paper towels and top with a rack.
2. In a medium pot, heat 3 inches of oil to approximately 365°. Meanwhile, in a medium bowl, combine the flour with 1/2 teaspoon salt. Whisk in the egg. Add the beer slowly, whisking.
3. Dip the pieces of cod, a few at a time, in the batter, and then put them in the oil. Cook until the fish is done and the crust is light brown, about 4 minutes for 3/4-inch thick fillets. Remove the fish with tongs and put the pieces on the rack to drain. Sprinkle salt over the hot fish and put the baking sheet in the oven. Repeat in batches with the remaining fish. Serve with the tartar sauce.
The Cod Clan
Atlantic pollack, haddock, and hake are among the members of the extensive cod family. Although these fish vary slightly in terms of texture and flavor, one can generally be substituted for another. Small cod are often called scrod and can certainly be used here.
Wine Recommendation: Beer is a natural choice to drink with fried fish. If you opt to drink wine, look for one that will mimic beer's palate-cleansing qualities. Try a reasonably priced sparkling wine or an acidic white such as a pinot grigio from Italy.