Bring a large pan of salted water to the boil. Peel the potatoes and roughly chop them. When the water is boiling, add them and simmer for 20-25 mins till the potatoes are tender.

Meanwhile, put a smaller pan of water on to boil. Add the eggs to the pan and simmer for 8 mins. Drain the eggs and cover with cold water to stop them cooking. Set aside to cool.

Trim the roots and woody greens from the leeks. Finely slice them. Melt 50g butter in a pan and add the sliced leeks. Season with salt and pepper. Fry over a medium-low heat, stirring often, for 7-8 mins till the leeks are soft. Don't let them brown too much. Turn the heat down and add a splash of water if they're browning too quickly.

Add the cornflour to the leeks. Cook, stirring constantly, for 2 mins. Add a splash of milk to the leeks and stir till smoothly combined. Repeat, adding the milk little by little, till you have a smooth sauce. This should take around 3-4 mins.

Drop in the bouquet garni. Turn the heat up a little and bring the sauce to a simmer. Then turn the heat down and gently cook 4-5 mins till the sauce has thickened a little.

Preheat your oven to 180°C/Fan 160°C/Gas 4. The potatoes should've cooked for 20-25 mins by now. Check if they're tender. If so, drain them and shake off any excess water. Return to the pan and add 150g butter and a pinch of salt. Mash till smooth. Set aside, with the lid on, for later.

Meanwhile, finely grate the zest from the lemon. Rinse the baby leaf spinach.

When the sauce is ready, lift out the bouquet garni. Add the lemon zest and the spinach. Stir to wilt the spinach. Taste the sauce and add salt and pepper, if you think it needs it.

Arrange the fish pie mix in an 4 ltr ovenproof dish. Drain the eggs and peel them. Halve them. Tuck them into the dish with the fish pie mix. Pour over the spinach sauce.

Spoon the mash over the top of the fish pie. Coarsely grate 100g of the Cheddar and sprinkle it over the top of the pie. Bake for 40 mins till golden brown and bubbling. Serve with seasonal green veg.

Get Ahead^ You can assemble the fish pie the day before you want to bake it. Once you have topped it with the mash and cheese, transfer to the fridge and store overnight. When you're baking it, allow and extra 5-10 mins to ensure it is piping hot all the way through.