• 3.5 tsp. Diamond Crystal or 1¾ Morton kosher salt, divided, plus
• 0.5 cup panko
• 0.5 cup (packed) parsley leaves with tender stems, plus more for serving
• 3 Tbsp. extra-virgin olive oil, divided
• 1.5 lb. baby potatoes, halved if large
• Freshly ground pepper
• 1 2-lb. skinless cod, halibut, or haddock fillet
• 0.33 cup mayonnaise, plus more for fish
Steps
Step 1Place a rack in middle of oven; preheat to 425°. Using a vegetable peeler, remove zest from 1 large lemon in wide strips, leaving as much white pith behind as possible. Cut lemon in half and squeeze 2 Tbsp. juice from a half into a small bowl; set aside. Cut remaining lemon half into wedges and set aside for serving.
Step 2Process lemon zest, 4 oz. smoked Spanish chorizo, coarsely chopped, 2 oz. Parmesan, rind removed, coarsely chopped, 1 tsp. fennel seeds, 4 garlic cloves, and 1½ tsp. Diamond Crystal or ¾ tsp. Morton kosher salt in food processor until chorizo and Parmesan are finely chopped (chorizo pieces should be no bigger than a lentil). Add ½ cup panko, ½ cup (packed) parsley leaves with tender stems, and 1 Tbsp. extra-virgin olive oil; pulse until parsley is coarsely chopped.
Step 3Toss 1½ lb. baby potatoes, halved if large, a generous amount of freshly ground pepper, remaining 2 Tbsp. extra-virgin olive oil, and 2 tsp. Diamond Crystal or 1 tsp. Morton kosher salt on a large rimmed baking sheet to coat. Push to edges.
Step 4Pat one 2-lb. skinless cod, halibut, or haddock fillet dry; place in center of baking sheet. Using an offset spatula or butter knife, spread a thin layer of mayonnaise (about 2 tsp.) over fish. Scatter breadcrumb mixture on top, patting gently to adhere (cover top entirely, but don’t worry about sides). Roast until breadcrumbs are golden brown and potatoes are fork-tender, 18–20 minutes. Let rest 5 minutes.
Step 5Stir a large pinch of salt, reserved 2 Tbsp. lemon juice, remaining 1 garlic clove, finely chopped, and ⅓ cup mayonnaise in a small bowl to combine. Season sauce with more salt if needed.
Step 6Top fish with parsley. Serve with sauce and lemon wedges for
squeezing over.
