Quick fish and rosti pie

Method

1. Preheat the oven to 200°C/fan180°C/gas 6. Melt 30g butter in a medium saucepan and add the leeks. Cook for 1 minute, then stir in the flour and continue to cook over a medium heat for 1 minute, stirring constantly. Gradually stir in the milk. Bring to the boil then simmer, still stirring, for 2 minutes.
2. Add the seafood and pesto, season well and divide between 4 x 350ml ovenproof dishes.
3. Divide the potato rostis between the dishes. Melt the remaining butter in the saucepan, drizzle over the rosti, then season and bake for 15 minutes, until bubbling.
4. Pop under the grill for 4 minutes, until golden brown, and serve hot.