This is a classic New England sandwich with a few modern twists. The slaw is bright and crunchy and the sauce is made with real sour pickles and chopped capers, which gives it more dimension and less sweetness than traditional tartar sauce. The fish is fried with panko, which makes the exterior super crunchy, but the pillowy bun and the fish itself are soft and flavorful. It all comes together to make one of my favorite sandwiches of all time.
Technique tip: Make the coleslaw first so the vegetables have time to soak up the dressing and soften before the slaw is served.
In a small bowl, stir together the mustard, vinegar and sugar. Season with salt and pepper. Slowly whisk in the tablespoon of oil until well combined. Set aside.2.
In a large bowl, combine the cabbage, onion, carrots, radishes and parsley. Pour the dressing over the vegetables and toss to thoroughly combine. Season with more salt and pepper if desired and allow to sit for 30 minutes at room temperature, then refrigerate.3.
Meanwhile, in a small bowl, combine the mayonnaise, chives, lemon juice, capers, chopped pickle and a few dashes of hot sauce. Set aside.4.
In a wide shallow bowl, stir together the flour, 1 teaspoon salt, a generous pinch of pepper and the cayenne. Whisk the eggs and a pinch of salt in another shallow bowl. Combine the panko and a pinch of salt in a third shallow bowl.5.
Season both sides of the fillets lightly with salt and pepper. Dredge in the seasoned flour, shaking off excess. Dip in the eggs, letting excess drip off, then gently press into the panko to completely coat. Transfer the fillets to a large plate.6.
Place a 10- to 12-inch skillet over medium-high heat. Add enough oil so there is about 1/4-inch in the pan. When oil is hot, fry the fillets in 2 batches, turning once, until cooked through and crispy, 2-3 minutes per side. Drain each batch on a paper towel-lined plate.7.
To assemble sandwiches, spread 2 tablespoons of the mayonnaise mixture on each bottom bun, add a fillet, dress with the slaw and top with the top buns. Serve with any leftover sauce and slaw on the side.