Fish Pie

Ingredients

For the mashed potato

• 2 ½ lb floury potatoes, 1.1 kg, such as Russet or Maris Piper, peeled and cut into chunks
• 4 tbsp unsalted butter, 56 g
• ¼ cup whole milk, 60 ml, warm
• ½ cup Cheddar cheese, 50 g, grated
• ½ tsp fine salt

For the filling

• 2 ½ cups whole milk, 600 ml
• 1 bay leaf
• 8 oz salmon fillet, 225 g, skinless
• 8 oz smoked haddock, 225 g, skinless (undyed if possible)
• 8 oz cod or other white fish, 225 g, skinless
• 4 tbsp unsalted butter, 56 g
• 1 small leek or onion, finely chopped
• ⅓ cup all-purpose flour (plain flour), 40 g
• 1 tsp Dijon or English mustard
• 1 tbsp lemon juice
• 3 tbsp fresh parsley, chopped
• 2 tbsp fresh dill or chives, chopped
• ¼ tsp black pepper

Instructions

Make the mashed potato

1. Put the potatoes in a pot of cold salted water, bring to a boil and cook for 15 to 20 minutes, until tender. Drain well and mash with the butter, warm milk, Cheddar and salt until smooth.

Poach the fish

2. Heat the oven to 400°F (200°C, or 180°C (355°F) fan, gas mark 6).
3. Bring the milk and bay leaf to a gentle simmer in a wide pan. Add the fish and poach for 5 minutes, until just cooked. Lift out the fish, strain and reserve the milk.
4. Flake the fish into large chunks into a 2½-quart (2.5 L) baking dish, removing any bones.

Make the sauce and bake

5. Melt the butter in a saucepan and cook the leek for 5 minutes, until soft. Stir in the flour and cook for 1 minute.
6. Gradually whisk in the reserved milk and simmer, whisking, for 3 to 4 minutes, until thick. Stir in the mustard, lemon juice, herbs and pepper. Taste for salt; the smoked fish is salty.
7. Pour the sauce over the fish and stir gently. Let cool for 10 minutes.
8. Spoon the mashed potato over the filling, spread it to the edges and rough up the surface with a fork.
9. Bake for 25 to 30 minutes, until the filling is bubbling and the top is golden. Rest for 10 minutes before serving.