The sweetness of pumpkin loves earthy sage and the roasty flavour of toasted walnuts – it's a classic Italian combo for good reason. Here we use it to layer fresh sheets of pasta, alternating with ricotta and Parmesan, and topping the lasagne with Parmesan-enriched bechamel, resulting in a deeply comforting vegetarian dish, ready for the oven, that needs only a salad – ideally with a few bitter leaves like radicchio or endive – on the side.