Spiced Slow-Cooked Mushroom Pie with Celeriac and Cheddar Mash

This slow-cooked pie is packed with flavour from warming tagine spices; just leave it in a low oven and let it look after itself. Puy lentils add texture to the filling, and a crisp topping of celeriac, sweet potato and cheddar finishes the dish beautifully. My husband put his fork down after finishing this in record time, with the heartening feedback: ‘this pie is FIT’. He’s not wrong.