Fish Casserole with Cod, Vegetables and Mashed Potatoes Recipe
Fish casserole with cod, vegetables and mashed potatoes is a Polish, home‑style version of British fish pie. Instead of breaded fish with chips, you get tender pieces of cod in a vegetable sauce, covered with a thick layer of fluffy mash. It’s a great way to sneak fish into meals for children and for people who usually turn their noses up at fish dishes.
This fish casserole is a homely Polish answer to British fish pie – instead of a heavy breadcrumb coating you get delicate cod in a vegetable sauce under a blanket of fluffy mash. The creamy sauce with carrot, leek and peas gently surrounds the fish, so the flavour is subtle and friendly even for those who usually avoid fish dishes. It combines the comfort of mashed potatoes with light white fish, so it’s filling but not overwhelming.
Chef's tips
Poach the cod very gently – in barely simmering milk – so it doesn’t dry out or break down into mush when mixed with the sauce. Make the mashed potatoes on the thicker side rather than too loose; this way they form an appetising, slightly crisp top after baking. When thickening the sauce with flour, add the milk in small amounts and whisk vigorously to avoid lumps; if they do appear, you can quickly pass the sauce through a sieve.
How to serve
Serve the casserole with a simple sauerkraut slaw or pickled cucumbers to add acidity and cut through the creaminess. To drink, homemade compote or a mug of tea with lemon is perfect, especially on colder days. It’s a very good option for a Sunday family dinner when you want to serve fish in a form that children will accept.
Ingredients
- cod fillet skinless and boneless - 500 g
- potatoes for the mash - 800 g
- carrot medium - 2 pieces
- leek white part - 0.5 pieces
- milk for the sauce and mash - 300 ml
- butter for the sauce and mash - 40 g
- wheat flour for thickening the sauce - 1.5 tablespoons
- green peas frozen - 150 g
- salt for the potatoes, sauce and fish - 1.75 teaspoons
- black pepper - 0.5 teaspoons
- bay leaf - 1 piece
- dill chopped, optional - 2 tablespoons
Preparation
- Peel the potatoes, cut into smaller pieces, cover with cold water, add 1 teaspoon of salt and cook until tender (about 20 minutes from boiling). Drain, let them steam off briefly over low heat, add 25 g butter and about 100 ml milk, and mash until smooth. If needed, add a little more milk so the mash is fluffy.
- Preheat the oven to 190°C (top and bottom heat). Prepare an ovenproof dish with a capacity of about 2 litres.
- Peel the carrot and cut into small cubes. Wash the leek thoroughly and slice into half‑moons.
- In a pot bring 200 ml milk with the bay leaf to a boil. Reduce the heat, add the pieces of cod and poach over very low heat for 5–7 minutes, just until the fish turns opaque and starts to flake. Lift the fish out with a slotted spoon onto a plate; do not discard the milk.
- In a frying pan melt 15 g butter over medium heat. Add the carrot and leek and fry for 5–7 minutes, stirring, until the vegetables soften.
- Add the flour, mix thoroughly and fry for 1 minute until the flour is combined with the butter and vegetables.
- Gradually pour in the milk used to cook the fish, stirring constantly to avoid lumps. Cook for 3–4 minutes until the sauce thickens to the consistency of thick cream. If it is too thick, add a little extra milk.
- Add the frozen peas and cook for another 2–3 minutes until defrosted. Season the sauce with 0.75 teaspoon salt, pepper and, if using, chopped dill. Remove the bay leaf.
- Gently break the cod into larger chunks with your fingers or a fork, checking carefully for any bones.
- Spread the fish pieces over the bottom of the ovenproof dish. Pour the vegetable sauce over them so the fish is covered.
- Spread the mashed potatoes on top, smoothing with a spoon or making light ridges with a fork, which will brown nicely.
- Place the casserole in the preheated oven and bake for 20–25 minutes, until the top of the mash is lightly browned and the sauce is gently bubbling around the edges.
- After removing from the oven, leave the casserole to stand for 10 minutes so it’s easier to serve and the sauce thickens slightly.
Storage
Keep leftovers covered in the fridge for up to 2 days. Reheat in the oven, covered with foil, until hot in the centre; you can also reheat individual portions in the microwave. Do not refreeze once thawed if the casserole has already been frozen before baking.
