Crispy Topped Fish Pie

Ingredients

• 25g plain flour
• 150g frozen peas
• sea salt and black pepper, to taste
• 1 medium onion, finely chopped
• 300ml milk
• 50g butter
• 1 tbsp Dijon mustard
• 900g potatoes, peeled and chopped
• 100ml milk
• 25g butter
• 50g panko breadcrumbs
• 75g grated mature cheddar
• 15g fresh parsley, chopped
• 1 lemon (zest and a squeeze of juice)
• 600g cod and smoked haddock, chunked
• Dressed green salad, to serve

Method

1. Preheat the oven to 200°C fan. Tip the potatoes and celeriac into a pan of well-salted water — it should taste like the sea — and boil for 15–20 minutes until everything gives easily to the tip of a knife. Drain and let them steam-dry in the colander for a minute or two: water clinging to the potato means a gluey mash, and we want light and fluffy.
2. While the potatoes cook, melt 25g butter in a wide pan over medium heat and sweat the onion for about 6 minutes until soft and translucent with no colour — you're after sweetness, not browning. Scatter in the flour and cook for a full minute to take the raw edge off, then gradually whisk in the 300ml milk a splash at a time until smooth. Simmer for 3 minutes, stirring, until the sauce is thick and glossy and coats the back of a spoon.
3. Off the heat, stir in the Dijon, peas and lemon zest along with a squeeze of lemon juice — the acid cuts the richness of the milk and butter so the sauce tastes bright, not heavy. Season generously with salt and pepper.
4. Fold the chunked fish gently through the warm sauce and let it sit for 2–3 minutes — just until the edges turn opaque. Don't cook it through; it has 25 minutes in the oven still to come, and overcooked fish goes chalky.
5. Mash the drained potatoes and celeriac with the remaining 25g butter and the warmed 100ml milk until light and fluffy. Taste and season — properly. The mash needs to stand up on its own; bland mash on top of seasoned filling will read as bland pie.
6. Spoon the filling into a wide ovenproof dish. Spread the mash over the top, then drag a fork across to pull up rough peaks — those ridges are what go crisp and golden. Scatter the cheddar and panko evenly over the surface and dot with a few small flecks of butter.
7. Bake for 25–30 minutes until the top is deeply golden, the breadcrumbs are bronzed, and the filling is bubbling lazily at the edges. A skewer pushed into the centre should meet flaky fish and steaming sauce. Taste a spoonful of the sauce at the edge — adjust salt now, not at the table.
8. Rest for 5 minutes so the sauce settles and doesn't run when you cut in. Bring the pie to the table, scatter with chopped parsley, set the lemon wedges alongside for squeezing over each plate, and serve with a sharply dressed green salad.