Dinner

Rosti-Topped Fish Pie Recipe

Name: Rosti-Topped Fish Pie Recipe
Prep time: 15 min
Cook time: 20 min
Total time: 35 min
Cuisine: British
Ingredients: 300g waxy potatoes, halved; 250g skinless coley fillets (fresh or frozen); 300ml milk; 50g butter, divided; 1 leek, finely sliced; 25g flour; 2 tbsp chopped parsley; 2 tsp Dijon mustard; Salt, to taste; Freshly ground black pepper, to taste

ByJack Voss November 8, 2025November 8, 2025

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Introduction

This Rosti-topped fish pie is a comforting dish that combines tender white fish in a creamy mustard sauce with a crispy potato topping. It’s an easy, satisfying meal perfect for cozy dinners any night of the week.

A white square ceramic dish filled with a layered casserole topped by a golden-brown grated potato crust, slightly crispy and uneven with some browned bits, revealing a middle layer of creamy white sauce with small pieces of light chicken and thin slices of green vegetables peeking through. The dish sits on a white marbled surface along with a large silver spoon and a fork resting beside the dish. Photo taken with an iphone --ar 4:5 --v 7

Ingredients

300g waxy potatoes, halved
250g skinless coley fillets (fresh or frozen)
300ml milk
50g butter
1 leek, finely sliced
25g flour
2 tbsp chopped parsley
2 tsp Dijon mustard

Instructions

Step 1: Cook the potatoes in boiling salted water for 5 to 7 minutes until almost tender but still firm enough to grate. Drain and rinse under cold running water to cool. Set aside.
Step 2: Place the coley fillets in a shallow saucepan and pour over the milk. Bring to a gentle simmer and cook for 5 minutes. Drain the fish, reserving the milk, and set both aside.
Step 3: Heat half the butter in a medium saucepan over medium heat. Add the sliced leek and cook for 5 to 6 minutes until softened.
Step 4: Stir in the flour and cook for 1 minute, then remove the pan from the heat. Gradually add the reserved milk to the pan, stirring well between each addition.
Step 5: Return the pan to the heat and stir continuously until the sauce boils. Let it simmer gently for 2 minutes, then stir in the chopped parsley and Dijon mustard.
Step 6: Preheat the grill to high. Flake the cooked fish into large pieces and fold gently into the sauce. Transfer the mixture to a small ovenproof dish.
Step 7: Coarsely grate the cooled potatoes. Melt the remaining butter, toss the potatoes in it, season with salt and pepper, then scatter evenly over the fish mixture.
Step 8: Place the dish under a medium grill for 5 to 10 minutes, or until the potato topping is golden and tender. Serve hot.

Tips & Variations

Use waxy potatoes for the topping to achieve a crisp texture while keeping some softness inside.
Substitute coley with other white fish like cod or haddock if preferred.
For extra flavor, add a squeeze of lemon juice to the sauce before baking.
Mix some grated cheese into the potato topping for a richer finish.

Storage

Store any leftover pie covered in the refrigerator for up to 2 days. Reheat in the oven at 180°C (350°F) until warmed through, about 15-20 minutes, to keep the topping crispy. Avoid microwaving to prevent sogginess.