To make the Bolognese sauce, in a large and deep frying pan or a Dutch Oven heat 1 tbsp of olive oil and fry the diced pancetta or bacon, then add diced onions, carrots, celery, minced garlic and cook on low heat for 10 minutes without colouring the vegetables. Then add the ground beef and brown it until the beef is no longer pink inside while stirring the whole time and making sure to break up the beef. Pour in both types of canned tomatoes and water with a pinch of salt and pepper.
Sprinkle in some dried oregano and torn basil leaves (reserve a few small ones), bring everything to a boil. Then turn the heat down and let it simmer with a lid ajar for for 2-2.5 hours stirring it once in a while. You can make the sauce for up to 3 days ahead before assembling the lasagna.
Prepare the Bechamel sauce by melting the butter in a saucepan, then adding the flour. Stir to combine, then continue cooking the mixture while stirring until it smells slightly nutty. Gradually pour in milk while whisking to avoid lumps, season with salt, pepper and grated nutmeg. Cook the sauce over low heat until thickens for about 10 minutes. Set aside.
Preheat the oven to 180C/350F. To assemble the lasagne, spread a thin layer of the Bolognese sauce over the bottom of a 9X13 inch rectangular pan, which is deep enough to hold 3 layers of lasagne.
Then cover the sauce with the lasagna sheets followed by β
of the Bolognese sauce and β
of the Bechamel sauce directly on top the Bolognese. Then sprinkle the white sauce with 3-4 tablespoons of the freshly grated Parmesan cheese. Repeat this layering twice more finishing with the Bechamel sauce, grated Parmesan cheese and a few scattered basil leaves. (See process images for reference, you should have 3 layers in total.)
Cover the lasagne with aluminium foil and bake in the preheated oven for 30 minutes, then uncover and bake for 15 minutes longer or until the lasagne sheets are cooked all the way through and the top is golden. Let the lasagna sit for 20 minutes before cutting into it.