Celeriac is probably my favourite root. It is delicate, yet very nutty, and has an elegant oily smoothness. Like all good vegetables, it is marvellous simply with a bit of olive oil. Here it works with the lentils and nuts to create a hearty autumn main course. Serve it warm, with a radish, cucumber and dill salad dressed with soured cream and olive oil. Or, allow it to cool down, then take it to work for lunch or on a picnic.