I made this today for lunch and it's perfect for Saturday simplicity. I used Basa fillets and Crimini mushrooms only because I had them in the fridge. Use whatever white fish you have but I've found smoked fish is too strong. Mashed potatoes will soak up all the lovely leftover sauce and it saves you licking the plate!
575g White fish, skinned
2 tbsp Lemon juice
1 Onion, finely chopped
25g Plain flour
150ml fFsh stock
125ml Double cream
200g Mushrooms, finely sliced
Dash of Worcestershires sauce
125g Cheddar or Gruyere cheese, grated
Wash the fish and pat dry with kitchen roll. Cut the fish into bite-sized pieces. Sprinkle with the lemon juice and season. Set aside. Preheat the oven to 200 degrees C/400 degrees F/ Gas 6. To make the sauce, melt the butter over a low heat in a large saucepan. Add the onion, cook gently for 2 minutes. Sprinkle over the flour and cook gently for 1 minute, stirring constantly. Gradually add the milk and fish stock, stirring all the time so the sauce is smooth. Add the mushrooms then simmer for 5 minutes.
Stir as the sauce will thicken and you don't want it to burn. Stir in the cream and the fish, season to taste, add the Worcestershires sauce.
Spoon the mixture into a large gratin dish or any ovenproof dish and sprinkle the grated cheese over.
Bake for 30 minutes or until crisp and golden.