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Delicious easy fish pie topped with golden mashed potatoes, a classic British casserole.

Easy Fish Pie — British Creamy Baked Casserole

A creamy, comforting fish pie topped with fluffy mashed potatoes, perfect for cozy weeknight dinners.
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Prep Time 30 minutes
Cook Time 40 minutes
Total Time 1 hour 10 minutes
Servings: 4 servings
Course: Comfort Food, Dinner
Cuisine: British
Calories: 600
Ingredients Method Notes

Ingredients
  

Fish and Filling
  • 500 g mixed fish (cod, haddock, and salmon) Use frozen fish if easier, thaw it before use.
  • 1 cup frozen peas Optional.
  • 1 cup sweetcorn Optional.
  • 1 cup chopped spinach Optional.
Flavor Base
  • 50 g butter For cooking onions or leeks.
  • 1 medium onion or leek Chop finely.
  • 2 cloves garlic Optional, minced.
  • 1 tsp thyme A pinch for flavor.
Creamy Sauce
  • 50 g butter For the sauce.
  • 50 g flour For thickening the sauce.
  • 500 ml milk For a smooth sauce.
  • 1 tbsp Dijon mustard Optional, adds flavor.
Mashed Potato Topping
  • 800 g potatoes For mashing.
  • 50 g butter For the mash.
  • 100 ml warm milk For creamy consistency.
  • 1 tsp salt For seasoning.
  • 1 tsp pepper For seasoning.
  • 50 g cheddar cheese Optional, for topping.

Method
 

Preparation
  1. Boil and mash the potatoes until thick and fluffy.
  2. Cook onion or leeks in butter until soft.
  3. Stir in flour, then slowly add milk to create a smooth sauce.
  4. Season the sauce well, then add the fish and any optional extras (peas, sweetcorn, spinach).
Baking
  1. Spoon the mixture into a baking dish and let it cool for 5 minutes.
  2. Top with mashed potatoes and rough up the top with a fork for crispy ridges.
  3. Bake in the oven until golden and bubbling around the edges (about 30-40 minutes).

Notes

Let the pie rest for 10 minutes before serving to thicken the sauce. Leftovers can be refrigerated for up to 2 days; reheat in the oven for best results.