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 Recipe

Prep Time 20 minutes mins

Cook Time 35 minutes mins

Total Time 55 minutes mins

Servings 4

Cook ModeTurn this on to keep your screen awake while cooking

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. 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. 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. 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. 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. 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. 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. 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 is a gratin de poisson a.k.a. fish bake, which is fundamental to French home cooking. The technique is simple: layers of fish and vegetables bound with béchamel, topped with buttered breadcrumbs, baked until golden.

If you want to do it the proper French way, then don’t use cheese on your fish bake. That’s more of a British or American habit. Traditional French fish gratins rely on good béchamel and crispy breadcrumbs (chapelure) for texture and flavour. The breadcrumbs are mixed with butter and sometimes a bit of parsley, but that’s it.

Béchamel is one of the five French mother sauces, supposedly created by Louis de Béchamel, chief steward to Louis XIV, though Italian cooks had been making similar white sauces long before. The French just gave it a fancy name and made it official. A proper béchamel is smooth, creamy, and seasoned with nutmeg. It’s also used in the famous Croque Madame.

The potato layers make this more substantial, not traditional in every fish gratin, but practical. It stretches the fish further and stops it being just protein swimming in sauce. Very much in the spirit of French home cooking, where nothing’s wasted and meals need to fill people up without costing a fortune.