Anna Louise The classic fish pie on this site uses a mashed potato topping — creamy, golden, and completely traditional. This version uses a rosti topping instead — grated potato mixed with butter, pressed over the filling, and baked until deeply golden and shatteringly crispy on top, soft in the middle, and completely irresistible.
The rosti topping changes the entire character of the dish. Where the mash topping gives a gentle, creamy contrast to the fish filling, the rosti gives a dramatic textural difference — crispy and slightly crunchy on top, giving way to the rich, creamy fish filling beneath.
Every spoonful has the satisfying combination of crispy potato and silky sauce that makes this version genuinely exciting rather than simply comforting.
The fish filling is identical to the standard fish pie — white fish, smoked haddock, prawns in a cream sauce — with the same care for quality of fish and seasoning. The rosti topping is the one departure and it is a departure worth making.
Ingredients for Mary Berry Fish Pie with Rosti Topping
For the Fish Filling
- 300g skinless cod or haddock fillet, in large chunks
- 200g skinless smoked haddock fillet, in large chunks
- 200g large raw king prawns, peeled
- 600ml whole milk
- 1 bay leaf, 6 black peppercorns, a slice of lemon
For the Cream Sauce
- 50g unsalted butter
- 50g plain flour
- The strained poaching milk (approximately 550ml)
- 150ml double cream
- 1 tsp Dijon mustard
- 2 tbsp fresh dill, chopped
- 2 tbsp fresh flat-leaf parsley, chopped
- Juice of ½ lemon
- Salt and freshly ground white pepper
For the Rosti Topping
- 900g floury potatoes (Maris Piper), peeled
- 75g unsalted butter, melted
- Salt and white pepper
- 50g mature Cheddar, finely grated — scattered over the top (optional)
How to Make Mary Berry Fish Pie with Rosti Topping
Step 1 — Poach the White Fish and Smoked Haddock
Place the white fish and smoked haddock in a wide, shallow pan. Pour over the milk. Add the bay leaf, peppercorns, and lemon slice. Bring to a very gentle simmer and poach for five to six minutes until just beginning to flake. Lift out carefully with a slotted spoon. Strain and reserve all the poaching milk.
The prawns do not need poaching — they will cook in the oven.
Step 2 — Make the Cream Sauce
Melt the butter in a large saucepan over a medium heat. Add the flour and stir for two minutes. Add the warm poaching milk gradually, whisking continuously until smooth. Add the cream and mustard. Bring to a gentle simmer and cook for five minutes until thick and glossy. Add the dill, parsley, and lemon juice. Season carefully with salt and white pepper.
Step 3 — Combine the Filling
Preheat your oven to 200°C / 180°C fan / Gas 6.
Gently fold the poached fish and raw prawns into the sauce. Transfer to a large, deep ovenproof dish approximately 30x20cm. Leave to cool for ten minutes while you make the rosti topping.
Step 4 — Make the Rosti Topping
Coarsely grate the peeled raw potatoes directly onto a clean tea towel or muslin. Gather the towel and wring firmly to extract as much moisture as possible — squeeze in batches if needed. This step is the most important for a crispy rosti. The drier the grated potato, the crispier the finished topping.
Transfer the wrung-out potato to a bowl. Add the melted butter. Season very generously with salt and white pepper. Toss to coat every strand evenly.
Step 5 — Top and Bake
Spread the grated potato topping evenly over the fish filling — pressing lightly to cover the surface completely from edge to edge. The topping should be about 1.5cm thick across the surface.
Scatter the grated Cheddar over the top if using.
Bake for 35 to 40 minutes until the rosti topping is deeply golden and crispy on top and the filling is bubbling at the edges. If the top is golden but the filling does not seem hot enough, cover loosely with foil and give it five more minutes.
Step 6 — Rest and Serve
Leave to stand for five minutes before serving. The filling needs a moment to settle.
My Top Tips For Perfect Fish Pie with Rosti Topping
Wring the grated potato as dry as possible. This is the single most important step for a crispy rosti topping. A wet rosti steams rather than crisps and gives a pale, soft, slightly soggy top rather than a deeply golden, crunchy one. Wring in a clean tea towel, gathering the corners and twisting, until no more liquid comes out. Do it twice if in doubt.
Season the rosti topping very generously. The potato absorbs a significant amount of seasoning during the wringing and the subsequent baking. Under-seasoned rosti topping tastes bland against the well-seasoned fish filling below. Season until it tastes slightly more assertively than you want the finished dish to be.
Cool the fish filling for ten minutes before adding the rosti. The same principle as the dauphinoise-topped cottage pie — hot filling rising through a potato topping can partially cook it from below before the oven does its work properly. Ten minutes of cooling gives the rosti a better, more even bake.
Use Maris Piper — not waxy potatoes. Floury potatoes like Maris Piper give a rosti topping that crisps beautifully. Waxy potatoes hold their moisture and resist crisping.
The Cheddar on top is optional but excellent. Scattered over the rosti before baking, it melts into the potato strands and crisps to golden patches that are completely delicious.
Serving Suggestions
With steamed peas or green beans alongside. With a simple green salad for freshness. On its own — the rosti topping and fish filling together are a complete meal.
How to Store
In the fridge: Store covered for up to 2 days. Reheat uncovered in a 190°C oven for 15 to 20 minutes to restore the crispness of the rosti.
In the freezer: Freeze before baking for up to 2 months. Cover tightly. Defrost overnight and bake as directed, adding ten minutes.
Mary Berry Fish Pie with Rosti Topping Recipe
Ingredients
Method
- Poach white fish and smoked haddock in milk with bay leaf, peppercorns, and lemon — 5–6 minutes. Lift out carefully. Strain and reserve milk.
- Make cream sauce: melt butter, add flour, stir 2 minutes. Add warm poaching milk gradually — whisk smooth. Add cream and mustard. Simmer 5 minutes until thick. Add dill, parsley, and lemon juice. Season with salt and white pepper.
- Preheat oven to 200°C / 180°C fan / Gas 6. Fold fish and raw prawns into sauce — gently. Transfer to dish. Cool 10 minutes.
- Coarsely grate raw peeled potatoes. Wring very thoroughly in a clean tea towel until completely dry. Transfer to bowl. Add melted butter — season very generously. Toss to coat.
- Spread rosti topping evenly over fish filling — press lightly to cover completely. Scatter Cheddar if using. Bake 35–40 minutes until rosti is deeply golden and crispy and filling is bubbling.
- Rest 5 minutes. Serve immediately.
Notes
Frequently Asked Questions
Can I use sweet potato for the rosti topping?
Yes — sweet potato gives a slightly sweeter, more golden rosti with a beautiful colour. It releases slightly more moisture than regular potato — wring even more thoroughly.
Can I add salmon to the filling?
Yes — 150g of fresh salmon fillet poached with the other fish and flaked into the filling gives a richer, more varied result. See the luxury fish pie recipe for a version with salmon and scallops.
Can I make the rosti topping ahead?
Yes — grate, wring, and season the potato up to two hours ahead. Store in a covered bowl in the fridge. Toss in melted butter just before topping the pie.
Why is my rosti topping pale instead of golden?
Either the potato was not wrung dry enough, or the oven temperature was not high enough. Make sure the oven is fully preheated to 200°C and the potato was thoroughly dried before use.
Leave a Reply