Peel and chop potatoes into even chunks.
Put them in a large pot of water.
Add a pinch of salt to water.
Bring to a boil over high heat.
Reduce heat and simmer for 15 minutes.
Check if they're soft with a fork.
Drain the potatoes in a colander.
Return them to the hot pot briefly.
This dries them out for better mashing.
Pour milk into a medium saucepan.
Add the white fish and smoked haddock.
Bring to a gentle simmer, not boiling.
Cook for 5 minutes until fish flakes easily.
Remove fish with a slotted spoon carefully.
Keep the milk for making sauce later.
Break fish into large, chunky pieces.
Remove any bones you find while breaking.
Melt butter in the same saucepan.
Add flour and stir for 1 minute.
This creates a smooth paste called roux.
Slowly pour in the reserved poaching milk.
Whisk constantly to avoid any lumps.
Add the heavy cream and keep stirring.
Cook for 5 minutes until sauce thickens.
Season with salt, pepper, and lemon juice.
Stir in chopped parsley for freshness.
Put the fish pieces in your dish.
Add the raw prawns to the mixture.
Pour the creamy sauce over everything evenly.
Gently fold everything together with a spoon.
Make sure sauce coats all the fish.
Spread mixture evenly in the baking dish.
Add butter to the drained potatoes.
Pour in the warm milk gradually.
Mash until smooth and creamy with no lumps.
Season well with salt and pepper.
Stir in half the grated cheese.
The potatoes should be fluffy and light.
Preheat your oven to 200°C (400°F).
Spoon mashed potatoes over the fish mixture.
Spread potatoes evenly to cover everything completely.
Use a fork to create texture patterns.
This helps create a crispy top.
Sprinkle remaining cheese over the potatoes.
Bake for 25-30 minutes until golden.
The top should be crispy and bubbling.
Let it rest for 5 minutes before serving.