Big fan of this ATK recipe. A little labor intensive but not prohibitively.
4 large slices white sandwich bread , torn into small pieces
2 tablespoons unsalted butter, melted
Table salt and ground black pepper
2 tablespoons minced fresh parsley leaves
1 small shallot , minced (about 2 tablespoons) (I used red onion)
1/4 cup plus 5 tablespoons unbleached all-purpose flour
2 large eggs
2 teaspoons prepared horseradish
3 tablespoons mayonnaise
1/2 teaspoon paprika
1/4 teaspoon cayenne pepper
1 1/4 pounds thick white fish (I used Atlantic cod)
Adjust oven rack to middle position and heat oven to 350 degrees. Pulse bread, melted butter, 1/4 teaspoon salt, and 1/4 teaspoon pepper in food processor until bread is coarsely ground. Transfer to a rimmed baking sheet and bake until deep golden brown and dry, about 15 minutes, stirring twice. Cool crumbs to room temperature (it takes about 10 minutes). Transfer crumbs to pie plate; toss with parsley and shallot. Increase oven temperature to 425 degrees.
Place 1/4 cup flour in second pie plate. In third pie plate, whisk eggs, horseradish (if using), mayonnaise, paprika, cayenne pepper (if using), and 1/4 teaspoon black pepper until combined; whisk in remaining 5 tablespoons flour until smooth.