Step 1

Adjust oven rack to middle position and heat oven to 450 degrees. Combine ¾ cup mayonnaise, pickles, pickle juice, shallot, capers, ¼ teaspoon salt, and ¼ teaspoon pepper in bowl; set aside.

Step 2

Combine remaining ¼ cup mayonnaise, lemon juice, mustard, and cayenne in second bowl. Pat fish dry with paper towels and season with pepper. Brush top and sides of fish with mayonnaise–lemon juice mixture and coat with potato chips, pressing to adhere.

Step 3

Place fish on foil-lined rimmed baking sheet and bake until fish flakes apart when gently prodded with paring knife and registers 140 degrees, 12 to 15 minutes. Serve with tartar sauce.