Bake the lasagne in two stages, as we do in Italy, so it stays firm when served. Heat the oven to 150C (130C fan)/300F/gas 2, bake for 25 minutes, remove and leave to cool; 40 minutes before serving, heat the oven to 200C (180C fan)/390F/gas 6, then re-bake the lasagne for 25 minutes more and take to the table.