• Squeeze the meat from the sausages and roll into meatballs – you’ll get about 4 balls from each sausage. Heat 1 tbsp of the olive oil in a large frying pan or shallow casserole dish on a medium to high heat. Cook the meatballs in batches, making sure you don’t overcrowd the pan, for 4 to 5 minutes until they’re all golden brown all over. Put them aside on a plate when they’re ready.
• Heat the rest of the olive oil in the pan and add the onion. Cook on a medium heat, stirring occasionally, for 8 to 10 minutes until soft, then stir in the garlic, fennel, oregano, and chilli flakes, if using. Stir around for a minute or 2, then add the sugar, passata and tomatoes. Add a little water to the tomato tin to wash out all the tomatoes and add to the pan. Season well and simmer, uncovered, for 30 to 40 minutes over a gentle heat, stirring occasionally, until the sauce thickens, and the chopped tomatoes break down. With 20 minutes left for the sauce to simmer, heat the oven to 190C/170C fan/gas 5.
• Melt the butter in a medium saucepan over a medium to low heat, add the bay leaves and let them sizzle in the butter for 1 minute, then add the flour.  Increase the heat slightly and using a whisk or wooden spurtle to make a smooth paste, add the milk, a little at a time, stirring continuously until it’s all incorporated and you have a thick white sauce. Add the nutmeg and some seasoning. Leave over a low heat for 5 minutes to allow the bay to infuse, whisking or stirring every now and then. Remove and discard the bay leaves.

To assemble:

• Keep about 10 meatballs aside and add the rest to the tomato sauce. Spoon half the tomato sauce and meatballs into a large baking dish (mine is 25cm x 35cm). Top with half the spinach, half the basil and a little parmesan. Pour over about a third of the white sauce, and top with a layer of lasagne sheets, breaking them up to fit the dish if you need to.
• Repeat the layers once more, meatballs and sauce, spinach, basil, parmesan, white sauce, pasta. Pour the remaining white sauce over the lasagne, spreading it to the corners to cover the pasta. Dot with the meatballs you set aside earlier and the mozzarella, then scatter over the rest of the parmesan and the cheddar.
• Bake the lasagne for 40 to 50 minutes until bubbling and golden with lots of crusty cheesy bits around the edges. Leave to sit for 5 to 10 minutes before serving. Or if not eating straight away, chill for up to 24 hours or freeze for two months (defrost in the fridge overnight before cooking).