Potato, Leek and Smoked Cheddar Pie

1. Preheat your oven to 200°C/Fan 180°C/Gas 6. Bring a large pot of salted water to the boil. Peel the potatoes and cut into 2cm cubes. When the water is boiling, tip in the potatoes and cook for 8-10 mins till just tender. Drain and set aside.

2. Meanwhile, trim, peel and finely slice the onions.Trim the roots and woody greens off the leeks, rinse out any grit, then slice them into 1cm-thick rounds. Pick the thyme leaves off their woody sprigs and chop.

3. Warm a large frying pan on a medium-high heat. Drizzle in 1 tbsp olive oil. Add the onions and leeks. Season with a pinch of salt and fry, stirring often, for 6-8 mins till glossy and starting to soften.

4. While the onions and leeks cook, coarsely grate the Cheddar. Set aside. When the veg are soft, sprinkle in the cornflour. Cook, stirring, for 1 min. Gradually trickle in 480ml of the milk, stirring constantly. Bring the mixture to the boil and cook for 3-5 mins till the sauce has thickened.

5. Stir in the mustard and thyme leaves. Sprinkle in the Cheddar and stir till melted. Return the potatoes to the pan. Season generously with salt and pepper. Stir together and simmer for 5 mins.

6. While the pie filling is simmering, dust your work surface with a little flour. Unwrap the pastry and roll it into a large, thin piece ½cm thick (round or rectangular, depending on the shape of your pie dish,. Transfer the mixture from the frying pan to your chosen pie dish. Lay the pastry over the filling and either tuck down inside the dish or use a fork to press it to the edges of the dish to seal. Brush the top of the pastry with the remaining milk.

7. Slide the pie into the oven and bake for 20 mins till the top is golden and crisp. Divide the pie between 4 warm plates. Serve with your favourite greens.