Pat the haddock fillets dry with paper towels. If fillets are very thick, butterfly by slicing horizontally almost through and opening, or leave whole for jumbo portions.

Place fillets on a rimmed baking sheet or broiler pan lined with foil. Brush both sides lightly with olive oil. Season evenly with coarse salt, black pepper, lemon zest, and minced garlic, pressing seasonings gently so they adhere.

Butter-lemon topping

Make topping

In a small saucepan over low heat, melt the unsalted butter. Stir in lemon juice, white wine (if using), and Dijon mustard. Remove from heat and stir in the chopped parsley. Taste and adjust seasoning with a pinch of salt or extra lemon if desired.

Spoon about half of the warm butter-lemon mixture over the top of each seasoned haddock fillet, reserving the remainder for finishing after cooking.

Cook (broil or bake)

Broil (recommended for a broiled request)

Position an oven rack 4–6 inches from the broiler. Preheat the broiler on high. Place the broiler pan with fillets under the broiler and cook for 6–10 minutes, depending on thickness: aim for an internal temperature of 135–145°F (57–63°C) and opaque, easily flaked flesh. Rotate the pan halfway through if broiler heats unevenly. Watch closely to avoid burning the garlic or butter.

Bake (alternative)

Preheat oven to 400°F (200°C). Bake the fillets on the prepared sheet for 12–18 minutes (depending on thickness), until the fish is opaque and flakes easily with a fork. During the last 2 minutes you may switch to broil to lightly brown the top.

If using broil method, once the fish is nearly done, spoon the reserved butter-lemon mixture over each fillet and return under the broiler for 30–60 seconds to glaze. If baking, spoon the reserved mixture over fillets immediately after removing from the oven.

Finish & garnish

Transfer fillets to warmed plates. Sprinkle with extra chopped parsley, and serve with lemon wedges on the side. Offer additional salt and pepper at the table.

Serve immediately with sides of your choice (roasted potatoes, steamed vegetables, or a simple green salad).