Broccoli Fish Bake

Dinner

Flaky white fish baked with broccoli and potatoes in creamy béchamel, finished with golden, buttery breadcrumbs. This is French gratin technique at its best, layers of good ingredients cooked slowly until everything melds together and the top goes crispy.

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Prep Time 20 minutes mins

Cook Time 35 minutes mins

Total Time 55 minutes mins

Servings 4

Ingredients 

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For the casserole

• 500 gr cod haddock, or pollock work well too
• 300 gr broccoli
• 2 waxy firm potatoes about 300g
• 50 gr breadcrumbs
• 30 gr unsalted butter
• squeeze lemon juice

For the béchamel

• 40 gr unsalted butter
• 40 gr plain flour
• 500 ml whole milk
• 1 tsp mustard Dijon
• 1 pinch nutmeg
• salt and black pepper

Equipment

1 baking dish

saucepan

whisk

knife

chopping board

mixing bowl

Instructions

1. Prep your ingredients

• Preheat your oven to 190°C (170°C fan). Butter your ovenproof dish generously. Cut the fish into large chunks, about 4cm pieces. You don't want them too small or they'll fall apart. Season with salt, pepper, and a squeeze of lemon. Cut the broccoli into florets, keeping them roughly the same size so they cook evenly. Slice your potatoes thinly, about 3mm thick. A mandoline makes this easier, but a sharp knife works too.

2. Blanch the broccoli and potatoes

• Bring a large pot of salted water to the boil. Blanch the potato slices for 3-4 minutes until they're just starting to soften but not cooked through. Scoop them out with a slotted spoon and set aside. Use the same water to blanch the broccoli for 2-3 minutes, it should still have a bit of bite. Drain well. This step means everything cooks evenly in the oven and you're not left with crunchy potatoes or mushy broccoli.

3. Make the béchamel

• Melt the butter in a saucepan over medium heat. Add the flour and whisk constantly for about a minute, this cooks out the raw flour taste. Gradually add the milk, whisking as you go to avoid lumps. Keep whisking until the sauce thickens enough to coat the back of a spoon, takes about 5-7 minutes. Add the mustard, nutmeg, and season with salt and white pepper. The sauce should be creamy but pourable, not thick like wallpaper paste.

4. Layer the casserole

• Start with a layer of potato slices on the bottom of your buttered dish, slightly overlapping. Add half the fish chunks, then half the broccoli florets. Pour over about a third of the béchamel sauce. Repeat with another layer of potatoes, the remaining fish, remaining broccoli, and another third of the sauce. Finish with any remaining potatoes on top, then pour over the last of the sauce, making sure everything's covered.

5. Prepare the breadcrumb topping

• Mix the breadcrumbs with the melted butter in a small bowl until all the crumbs are coated. This is what gives you that golden, crispy top. Scatter the buttered breadcrumbs evenly over the entire surface of the gratin. Don't press them down, just let them sit on top loosely.

6. Bake

• Bake for 30-35 minutes until the breadcrumbs are properly golden and crispy, and the sauce is bubbling around the edges. The fish should be cooked through and flake easily with a fork. If the breadcrumbs are browning too quickly, cover loosely with foil for the first 20 minutes, then remove it to let the top crisp up.

7. Rest and serve

• Let it sit for 5-10 minutes before serving. This gives the sauce time to settle and makes it easier to portion out without it collapsing into a mess on the plate. Serve with a simple green salad or some crusty bread to mop up the sauce.

Notes

• Any firm white fish works here, avoid oily fish like salmon or mackerel, which don’t suit the creamy sauce.
• Make your own breadcrumbs from stale bread if you can. They’re better than shop-bought and give you a more irregular, crispy texture.
• You can swap the broccoli for cauliflower, or use a mix of both.
• Add a handful of frozen peas in with the broccoli if you want extra veg.
• This keeps in the fridge for 2 days. Reheat covered with foil at 180°C for 20 minutes.
• For a richer version, replace 100ml of the milk with single cream.

About this recipe

This broccoli fish bake is French home cooking at its most practical and most satisfying. Layers of fish and vegetables, bound with béchamel, topped with buttered breadcrumbs, baked until golden. It’s the kind of dish that feeds a family without fuss and tastes like considerably more effort went into it than actually did.

What a gratin de poisson actually is

In France, this dish is called a gratin de poisson. The word “gratin” refers to the crust that forms on top during baking, from the French verb “gratter,” meaning to scrape. The crust is the point. Buttered breadcrumbs mixed with parsley, browned in the oven until crispy, are what separate a proper French fish bake recipe from just fish in sauce.

One thing to note if you want to do it the French way: no cheese on the fish. Melting cheese over fish is more of a British or American habit. Traditional French fish gratins rely entirely on good béchamel and crispy breadcrumbs for texture and richness. The béchamel does the work that cheese would do elsewhere, binding the layers and adding creaminess without competing with the flavour of the fish.

The béchamel

Béchamel is one of the five French mother sauces, the foundational sauces from which most of French cooking builds outwards. It’s supposedly named after Louis de Béchamel, chief steward to Louis XIV, though Italian cooks had been making similar white sauces long before the French gave it an official name and wrote it into their culinary canon.

A proper béchamel for this baked fish recipe is smooth, creamy, and seasoned with nutmeg. The nutmeg is not optional. It’s subtle, but without it the sauce tastes flat. The ratio of butter to flour to milk determines the thickness, and for a fish bake you want it slightly thicker than you’d use for a pasta dish so it holds the layers together during baking rather than running to the bottom of the dish.

Why this baked cod recipe works

Cod is the right fish for this dish. It’s firm enough to hold its shape through the baking process without falling apart into the sauce, and its clean, mild flavour works well with both broccoli and béchamel without being overwhelmed by either. This is a baked cod recipe that lets the fish stay recognisable in the finished dish rather than disappearing into the sauce.

The broccoli adds texture and colour, and it holds up well to oven heat without going mushy if you don’t overcook it in the initial blanching stage. Slightly underdone going into the dish is exactly right, as it continues cooking in the oven.

The potato layers make this more substantial, which is not traditional in every French fish gratin but is very much in the spirit of French home cooking. Potatoes stretch the fish further, add body to the dish, and mean it needs nothing alongside it except perhaps a green salad. Nothing wasted, everyone fed properly.

The right dish for baked fish

A good baked fish dish needs even heat distribution across the base and sides to cook the layers uniformly, and it needs to be deep enough to hold the béchamel without it bubbling over during baking. I use the Le Creuset baking dish for this fish bake recipe. The stoneware holds heat steadily throughout the bake, which means the béchamel stays at a consistent temperature and the breadcrumb crust browns evenly rather than catching in spots. It’s also the right size for four generous portions, and it goes straight from oven to table, which is the only sensible way to serve a gratin.

How the French eat this

In France, a fish bake like this is midweek food. Not a dinner party dish, not something you’d find on a restaurant menu, but the kind of thing that appears on a Tuesday when the weather has turned cold and everyone needs feeding properly. It reheats well the following day, the breadcrumb crust softens slightly but the flavour deepens overnight. It’s the kind of baked fish recipe that earns its place as a regular on the weekly menu.