Method
1. Half-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 but don’t chop them. When the water is boiling, add the whole potatoes and simmer for 10 mins.
2. While the potatoes cook, trim and discard the roots and woody greens from the leeks. Cut them in half, rinse out any grit and finely slice them. Trim and finely chop the carrots (there’s no need to peel them unless you prefer to). Trim and discard the dry ends from the celery sticks, then finely slice.
3. Drain the potatoes and set them aside in the colander. Put the pan back on a medium heat and add 1 tbsp oil and the prepared veg. Add a pinch of salt and pepper and fry, stirring often, for 8 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. Stir the mushrooms
and garlic into the veg and fry for 5 mins, stirring often, till the mushrooms look juicy.
5. Stir the lentils into the veg. Add the tomato ketchup and fischy sauce. Drop in the bay leaf and stir in 400ml hot water from the kettle. Cover, bring 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.
6. While the vegetables and lentils simmer, warm your oven to 200°C/Fan 180°C/Gas 6. Coarsely grate the cheddar and cooked potatoes. Pop them into a bowl with 1 tbsp oil and a pinch of salt and pepper, then toss to mix.
7. Taste the veg and lentils and add a pinch more salt or pepper, if needed. Ladle into a large ovenproof dish, then 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 with steamed green veg on the side.
8. 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. 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 loosely cover it with foil for the first 15 mins, then remove and bake for 20-30 mins till golden and bubbling.
9. Do The Mash
To make a mash topping, rather than a rösti topping, roughly chop the potatoes and boil them for 20 mins till tender. Make the lentil filling in a separate pan while the potatoes simmer. When the potatoes are tender, drain well, then tip them back into the pan, add 1 tbsp oil, some salt and pepper, and the grated cheese and mash until smooth.
10. Love Your Leftovers
Any leftover pie will keep in the fridge for up to 3 days, or you can freeze portions for up to 3 months. Divide the pie into tubs, cool and seal, then freeze or chill. Defrost overnight and reheat in the microwave till piping hot all the way through.