For the ragu: put the oil and pancetta in a large saucepan. Gently cook until the pancetta is crispy and golden. Add the onion and turn the heat down, cooking for about 10 minutes, until the onion is softened, then add the garlic and cook for a further 3 minutes.
Tip in the beef and pork minces and cook, breaking down the mince with the back of a wooden spoon then add the milk and chopped tomatoes. Stir in the bay leaves, rosemary, thyme, oregano, beef stock cube and wine, and bring to a simmer.
Cover with a lid and cook for 1 hr, stirring occasionally to stop the bottom catching, then remove the lid and gently simmer for another 30 mins-1 hr until the meat is tender and and the sauce has thickened. Taste and season then set aside to cool.
For the white sauce: melt the butter in a medium saucepan and once melted add the flour and mix into the butter. Cook the flour and butter mix for 2 minutes to cook out the raw flavour of the flour. Stir in the milk, a little at a time – adding milk gradually to avoid lumps.
When all the milk is in, bring to a simmer, stirring constantly until thickened, then stir in the cheeses and a good grating of nutmeg. Remove from the heat.
Preheat the oven to 200 C / 180 C fan.
To assemble: lay a large piece of baking paper on top of a large baking sheet. Lay the lasagne sheets on top of the baking sheet so that they are touching, and top with ½ of the cheddar and ½ of the mozzarella. Place this under the grill for 2 minutes to melt the cheese.
Once the cheese has melted, spread the sheet of lasagne with the meat sauce and drizzle over a little of the bechamel sauce then finish the grated parmesan. Roll the whole thing up like a swiss roll and place into a dish large enough to fit it. Pour over the remaining bechamel sauce and sprinkle with the remaining cheddar and mozzarella. Place into the oven for 30 minutes then remove and serve sprinkled with the remaining parmesan.