Classic Fish Bake

A classic fish bake is a one-pan casserole of white fish, vegetables, and a creamy sauce baked until the fish is opaque and the top is golden. It comes together quickly, tastes rich without much effort, and feeds four people from a single dish.

Ingredients for Classic Fish Bake

White fish fillets like cod or halibut are mild and cook through evenly in the oven. Potatoes provide substance and soak up the sauce. Onion and celery add savory depth, while frozen peas bring color and sweetness without watering down the dish. Butter and all-purpose flour make a roux that thickens the sauce to a creamy consistency. Whole milk creates that sauce, and fish or vegetable broth gives it body. Lemon juice brightens the flavors, while salt, black pepper, and dried thyme season the whole bake. Panko breadcrumbs and a little more butter scattered on top turn golden and crispy in the oven.

Why This Classic Fish Bake Works

Potatoes cook slowly, so they are sliced thin and layered on the bottom where they stay in direct contact with the hot pan. The sauce goes on top of them, which means the potatoes cook gently in liquid and become tender by the time the fish is done. If you used raw potatoes in a thick sauce without cooking them first, they would still be hard when the fish turns dry.

The fish sits on top of the potato layer where it cooks in just 12 to 15 minutes, so it stays moist and flakes apart when you press it with a fork. The sauce bubbles at the edges and thickens slightly as the oven heat works, and the breadcrumb topping browns in the last few minutes, giving you texture and a golden color.

Assembling everything takes less than 20 minutes, and you can build the whole casserole up to 24 hours ahead and bake it straight from the refrigerator without adding time. That makes this dish practical for weeknight dinner and flexible enough for company.

Mistakes To Avoid

Thick-sliced potatoes stay hard and starchy even after the fish is done. Slice them no thicker than 1/8 inch so the steam and sauce reach the center quickly and cook them all the way through.

Frozen peas added raw at the start turn mushy and dull by the time the bake is finished. Stir them in frozen just 5 minutes before the bake is done so they stay bright and hold their shape.

If the sauce is too thick, it dries out the fish and makes the whole casserole dense and gluey. The sauce should move slowly when you tilt the dish, not sit stiff like paste. Add more broth or milk a splash at a time if yours looks too stiff.

Leaving the breadcrumb topping on the whole time burns it dark brown and makes it taste bitter. Add it only in the last 8 to 10 minutes so it turns golden and crispy without charring.

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Ingredients

• 2 tablespoons butter
• 1 medium onion, diced
• 2 celery stalks, diced
• 2 tablespoons all-purpose flour (16g)
• 1 cup whole milk
• 1 cup fish or vegetable broth
• 1 pound potatoes, peeled and sliced thin
• 1.5 pounds white fish fillets, such as cod or halibut
• 1 cup frozen peas
• 1 tablespoon fresh lemon juice
• 1 teaspoon salt
• 1/2 teaspoon black pepper
• 1/2 teaspoon dried thyme
• 1/2 cup panko breadcrumbs
• 2 tablespoons butter, melted

Step-by-step Instructions

1. Preheat the oven to 400°F (200°C).
2. In a large skillet over medium heat, melt 2 tablespoons butter and add the diced onion and celery, cooking for 3 to 4 minutes until soft, stirring often.
3. Sprinkle the flour over the onion and celery, stir to coat, and cook for 1 minute until it no longer smells raw.
4. Pour in the milk and broth, stirring constantly, and simmer for 2 to 3 minutes until the sauce thickens slightly and coats the back of a spoon.
5. Stir in the salt, pepper, and thyme, then remove from heat and stir in the lemon juice.
6. Arrange the sliced potatoes in an even layer in a 9×13 baking pan, then pour half the sauce over them and stir gently to coat.
7. Lay the fish fillets on top of the potatoes and pour the remaining sauce over them.
8. Bake uncovered at 400°F (200°C) for 20 minutes until the sauce bubbles at the edges and the fish is opaque when you press it gently with a fork.
9. In a small bowl, mix the panko breadcrumbs with 2 tablespoons melted butter, then scatter the mixture evenly over the fish.
10. Bake for 8 to 10 minutes more until the breadcrumbs are golden brown and the fish reaches 145°F (63°C) in the thickest part.
11. Let rest for 5 minutes before serving so the casserole sets and holds together when you scoop it.