Preheat your oven to 200°C/Fan 180°C/Gas 6. Put a large pan of salted water on to boil.

Peel the potatoes and chop them into bite-sized chunks. As soon as the water in the pan is boiling, add the potatoes. Cover the pan with a lid and simmer for 15 mins, till the potatoes are tender and can be easily crushed with a fork.

Meanwhile, trim the roots and top 3cm off the leeks. Slice them in half, rinse out any grit and thinly slice them. Scrub the carrot and finely dice it (no need to peel it unless you prefer to). Peel the garlic and finely chop it. Roughly chop the chervil leaves and stalks.

Pour 1 tbsp olive oil into a deep frying pan or wok and warm it to a medium heat. Add the leek, carrot, garlic and a pinch of salt and pepper. Cover the pan and cook for 10 mins, stirring once or twice, till the veg have softened.

Stir 2 tbsp flour into the veg and cook, stirring, for 2 mins. Pour in around 100ml of milk and stir till smooth. Slowly pour in another 300ml milk and stir well to mix. Take the pan off the heat and stir in the chervil and the fish pie mix. Grate in the zest from the lemon. Scoop the fish pie filling into an ovenproof dish.

When the potatoes are cooked, drain them and steam dry in the colander for 1 min. Tip the potatoes back into the pan and pour in the remaining 100ml milk. Add a pinch of salt and pepper and mash till smooth. Dollop the mash over the fish pie filling and use a fork to smooth it into an even layer. Slide the pie into the oven and bake for 20-25 mins, till golden and bubbling.

While the pie is baking, trim the dry ends off the Tenderstem® broccoli stalks. Fill and boil the kettle, then fill the empty potato pan with hot water and return it to the boil. When the pie is almost ready, add the broccoli to the boiling water. Cook for 3-4 mins till tender, then drain.

Divide the fish pie and broccoli between a couple of warm plates. Serve with wedges of the zested lemon for squeezing.