Preheat your oven to 240°C/220°C fan/gas mark 9. Bring a large saucepan of water to the boil with ½ tsp salt.

Peel the potatoes and chop into 2cm chunks. Trim the root and dark green leafy part from the leek and discard. Halve lengthways, then thinly slice.

Peel and grate the garlic (or use a garlic press). Grate the Cheddar cheese.

Pat the cod dry with kitchen paper, then cut into 2cm chunks. IMPORTANT: Wash your hands and equipment after handling raw fish.

Once your pan of water is boiling, add the potatoes and cook until you can easily slip a knife through, 15-20 mins.

Meanwhile, heat a drizzle of oil and half the butter in a large frying pan on medium-high heat.

Allow the butter to melt, then add the leek. Stir-fry until softened, 3-4 mins, then stir in the flour (see pantry for amount) and cook, stirring frequently, until it forms a paste, 1-2 mins.

Stir in the water for the sauce (see pantry for amount) a little at a time, then add the veg stock paste and bring to the boil, stirring continuously. Reduce the heat and simmer, stirring occasionally, until thickened, 1-2 mins.

Once the sauce has thickened, stir through the creme fraiche and simmer for 3-4 mins.

Taste and season with salt and pepper if needed. Drain the prawns.

Next stir in the cod chunks and prawns until combined and pour the mixture into an appropriately sized ovenproof dish. IMPORTANT: Wash your hands and equipment after handling raw fish.

Once the potatoes are cooked, drain in a colander and return to the pan, off the heat. Add the remaining butter and a splash of milk (if you have any) and mash until smooth. Season with salt and pepper.

Spoon the mash on top of the fish mixture in an even layer.

Sprinkle over the grated cheese, then bake on the top shelf of your oven until golden, 10-12 mins. TIP: Put the dish onto a baking tray to catch any drips. IMPORTANT: The fish is cooked when opaque in the middle.

While the pie bakes, trim the green beans.

Wipe out your (now empty) frying pan and pop on medium-high heat with a drizzle of oil. 

Once hot, add the green beans and stir-fry until starting to char, 2-3 mins.

Stir in the garlic, turn the heat down to medium and cook for 1 min, then add a splash of water and immediately cover with a lid or some foil. Cook until tender, 4-5 mins. Remove from the heat.

When everything's ready, spoon the fish pie into bowls or onto plates.

Serve with the garlicky green beans alongside.