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.

Pin recipe Print

Prep Time 20 minutes mins

Cook Time 35 minutes mins

Total Time 55 minutes mins

Servings 4

Ingredients 

1x2x3x?

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

When you need a dish that feeds the whole family without any stress, this broccoli fish bake is exactly it. It’s French home cooking at its best, practical, satisfying, and so tasty. You layer fish with vegetables, pour over béchamel sauce, scatter buttered breadcrumbs on top, and bake until everything’s golden and bubbling. That crusty top with that creamy filling underneath? It’s food that makes everyone happy.

What a gratin de poisson actually is

In France they call this a “gratin de poisson”. The word “gratin” means that beautiful crust you get on top when it bakes. It comes from “gratter” which means to scrape, because everyone always wants to scrape up those crispy bits. That golden breadcrumb crust mixed with parsley and butter is what makes it special. It’s not just fish sitting in sauce, it’s that extra crunch that makes this French fish bake recipe irresistible.

Here’s something important if you want to do it the authentic French way, don’t scatter cheese on top of the fish. In France, traditional fish gratins stick to béchamel and breadcrumbs. The béchamel gives you that creamy richness and binds everything together, the breadcrumbs give you crunch, and together they let the fish flavour shine through instead of getting buried if you know what I mean.

The béchamel

Béchamel is one of the five French mother sauces. It’s like the foundation everything else builds on. They say it’s named after Louis de Béchamel who worked for Louis XIV, but Italian cooks were making white sauce long before that. Doesn’t matter who named it—it’s essential.

For this fish bake you want your béchamel smooth, creamy, and seasoned with nutmeg. Don’t skip the nutmeg. It’s subtle but makes the sauce taste finished instead of flat. The butter-flour-milk ratio controls how thick it gets. For fish you want it a bit thicker than you’d use for pasta. That way it coats everything nicely and holds the layers together instead of pooling at the bottom.

Why this baked cod recipe works

This baked cod recipe chooses cod fish because it stays firm through baking and it doesn’t break apart into mush in the sauce. Its mild, clean flavour plays well with broccoli and béchamel without getting lost. You still taste the fish when it’s done, not just sauce.

The broccoli gives colour and texture. It holds up to oven heat if you don’t over-blanch it first. Slightly underdone going into the dish is exactly right, it finishes cooking in the oven perfectly.

Potatoes make any dish hearty, this baked fish dish too! Not every French fish gratin has them, but it fits that practical home cooking spirit completely. Potatoes stretch the expensive fish further. They add substance so the dish feels complete and you feel full after eating it. You barely need anything alongside it, a simple green salad will do the trick. Nothing gets wasted and everyone leaves the table satisfied.

The right dish for baked fish

Your baking dish matters for fish gratins. You need even heat distribution and deep enough sides so the béchamel doesn’t bubble over. I always use the Le Creuset baking dish. The stoneware holds heat so steady, the béchamel cooks evenly and the breadcrumbs brown perfectly without burning in spots. It’s just the right size for four generous portions too. Best part? It goes straight from oven to table. That’s the proper way to serve a gratin, still bubbling, still fragrant.

How the French eat this

In France this broccoli fish bake is great midweek food. No, it’s not super fancy, but it’s tasty and satisfying for a random Tuesday dinner. It also makes great leftovers too, the flavours actually get better overnight even though the crust softens a bit. That’s why it earns a regular spot on the weekly rotation.