1. Fill and boil your kettle, then fill a large pan with the hot water, topping it up if needed. Add a pinch of salt, set the pan on a high heat and bring back to the boil. Meanwhile, peel the potatoes. When the water is boiling, add the whole potatoes and simmer for 10 mins. (Boiling them whole is perfect for making rösti, but if you’d prefer a traditional mash topping, see our tip). After 10 mins, drain the potatoes and set them aside in the colander. Keep the pan, ready to make the filling.
2. While the potatoes simmer, peel and finely chop the onions. Trim the roots and woody greens off the leeks, then halve them and rinse out any grit. Finely slice the leeks. Trim, peel and finely chop the carrots. Trim the dry ends off the celery sticks, then finely slice them.
3. Put the pan back on a medium heat and add 1 tbsp olive oil and the veg. Add a pinch of salt and pepper and fry, stirring often, for 8-10 mins till the veg look glossy and are starting to soften.
4. While the veg fry, rinse the mushrooms and tear them into small pieces. Peel and grate or crush the garlic. Drain and rinse the lentils.
5. Stir the mushrooms and garlic into the veg. Fry for 5 mins, stirring often, till the mushrooms look juicy. Fill and boil your kettle again. Preheat your oven to 200°C/Fan 180°C/Gas 6.
6. Stir the lentils into the veg. Add the tomato ketchup and 1 tbsp Worcester sauce. Drop in the bouquet garni (you can tie the herbs together to make them easier to fish out later). Stir in 400ml hot water from the kettle. Cover, bring the to a boil, then turn the heat down and simmer for 10-15 mins, stirring now and then, till the sauce has thickened and the veg are tender.
7. While the veg and lentils simmer, coarsely grate the cheddar, then coarsely grate the potatoes. Pop them in a bowl together and add 1 tbsp olive oil and a pinch of salt and pepper. Toss to mix.
8. Taste the veg and lentils and add a pinch more salt or pepper, if needed. Fish out the bouquet garni and discard it. Ladle the pie filling into a large ovenproof dish. Scatter the potatoes and cheese over the top. Slide the dish into the oven and bake for 20-25 mins till golden brown and bubbling. Serve the shepherdess pie in warm bowls.
9. Top Topping
To make a mash topping, rather than a rösti topping, roughly chop the potatoes and boil them for 20-25 mins till tender. You'll need to make the lentil filling in a separate pan while the potatoes simmer. When the potatoes are cooked through, drain them, tip them back into the pan, add 1 tbsp oil, some salt and pepper, and the grated cheese and mash.
10. Get Ahead
You can boil the potatoes the night before, cool them, and then store them in a tub or covered bowl in the fridge ready to grate and top the pie filling. You can also assemble the pie the night before cooking. Make the filling and the rösti topping, assemble the pie in a dish and store in the fridge, ready to bake. The pie will take a little longer to bake from the fridge, so cover it with a loose layer of foil for the first 15 mins, then remove and bake for 20-30 mins till golden and bubbling.