||To make the meat sauce; Heat a large, deep-sided frypan, ensure it is hot. Crumble in half of the mince. Cook the mince, breaking up any lumps with a fork. Let the liquid evaporate. Remove the first batch, reheat pan and cook remaining mince and then remove. Add oil, onion, carrot and celery to frypan, cook over a medium to low heat until onion is just soft.
||Return the mince to the frypan and add the tomato passata, water, herbs and season with salt, pepper and a small pinch of sugar. Bring to the boil, reduce heat to low, partly cover and simmer for 30 to 40 minutes. Add a little water to sauce if needed as it cooks.
||To make the white sauce; heat the butter in a saucepan over a medium heat, add flour and stir to combine, cook for 30 seconds. Add the milk gradually, stir until smooth. Add nutmeg, and season with salt and pepper. Stir constantly until the mixture boils and thickens. Remove from heat.
||To assemble lasagne; Preheat oven to moderate 180ºC. Use a deep, rectangular ovenproof dish (we used one 31 x 23cm). Add a couple of tbsp of meat sauce to the base of the dish, spread it out. Add a layer of lasagne sheets, top with some meat sauce, add a couple of tbsp of white sauce and spread it out over the meat.
||Continue in this way finishing with the white sauce. Sprinkle with Parmesan and a few tsp of butter. Bake covered for 20 minutes, and then uncovered for a further 20 minutes, or until thoroughly hot. Remove from oven and stand for 10 minutes before serving. Sprinkle with the extra Parmesan to serve.