Directions

1. Heat oven to 150C/130C fan/gas 2. For the meat sauce, heat the butter in a largecasserole dish. Scatter in the pancetta and sizzle gently for 5 mins until just starting to brown, then add the onion and carrot and soften in the pancetta fat for a few mins. Stir in the meat. At first it will look as if it's just steaming, but persevere and the juices will evaporate and the meat will sizzle and start to brown - this will take around 15 mins. When the beef is brown, add the garlic, bay leaf, oregano and some pepper and cook for 5 mins, then add the ketchup and cook to a paste. Season, pour over the wine and the passata, give everything a stir, bring to a simmer, then cover and place in the oven for 2 hrs, stirring occasionally until the meat is really tender.The sauce can be prepared up to three days ahead or frozen for three months.
2. For the white sauce, pour the milk into asaucepanwith the dried mushrooms, bring to the boil, then turn off the heat and leave the mushrooms to soak for 20 mins. Drain the mushrooms over a bowl, pressing down to release all the milk. Reserve the milk, roughly chop the mushrooms and set aside. Heat two-thirds of the butter in a large, shallow pan until it starts to turn a nutty brown. Add the mushrooms and a bay leaf, and sizzle for a few mins. Scatter the flour over the mushrooms and cook until it's a sticky paste. Gradually add the milk, stirring between each addition, until you have a thick sauce. Add the parmesan rinds if you have them, then simmer for 10 mins, stirring occasionally. Remove from the heat, lift out the bay leaf and any rinds, then stir in the mascarpone and a third of the parmesan. Season with salt, pepper and grate in some nutmeg.
3. Rub oil onto the base and sides of a large ceramic baking dish. Put a layer of lasagne sheets on the base, then a layer of the meat sauce, followed by a drizzle of mushroom sauce, and then tear and scatter over the mozzarella. Repeat until you have used all the pasta and meat sauce and top with a final layer of pasta. Finish with a thick layer of mushroom sauce and sprinkle with a layer of parmesan, reserving a handful. Scatter the remaining parmesan over a non-stick baking sheet or a baking sheet lined with baking parchment.
4. Heat oven to 200C/180C fan/gas 6. Bake the lasagne in the oven for 40-45 mins or until bubbling and golden brown. For the last 15 mins, put the parmesan tray in the oven on a higher shelf and cook until brown and crisp. Remove both from the oven and leave for 10 mins. Cut the lasagne into squares and let it sit for another 10 mins before serving to keep the layers defined and help it cool. Break the crispy parmesan into shards and serve in a side dish to scatter over the lasagne.