Preheat the oven to 190°C.
Butter the lasagne pan well and add a very thin layer of meat sauce.
Add the first layer of lasagne sheets and in order, cover with meat sauce, about 3 ladles Besciamella, and a generous sprinkle of Parmesan cheese. Repeat the same process until you reach the top of the dish. Make sure the lasagne sheets are soaking into the sauce.
When done layering the ingredients, top the lasagne with a final ladle of meat sauce and some Besciamella, add a few thin slices of butter and finish with some grated Parmesan.
Bake for about 30 minutes.
Heat the grill. When your fantastic Lasagne alla Bolognese is cooked, give it a nice crisp top by grilling it for about 5 minutes.
Always serve this dish with extra-virgin olive oil and some grated Parmesan, to taste.
For the Bolognese Sauce:
Saute the onion, carrots, and celery in about 5 tablespoons olive oil in a large rondeau until soft. Add the pancetta to the soffritto (onion mixture). Cook on a medium-high flame for about 7 to 10 minutes, then add the meat; break it up well with a wooden spoon. Cook's Note: You can jack up the heat a bit, and keep stirring until all the ground meat is browned. Add the red pepper flakes and the parsley and cook for just 1 minute.
Add the wine now and cook until the alcohol is completely evaporated, scraping up the browned bits on the bottom of the pan.
Pulse the tomatoes smooth in a food processor and add them to the meat, season generously with salt and pepper, lower the flame to medium and cook for about 2 1/2 hours, stirring occasionally. Finish the sauce by adding the whole milk, stir well and set aside, to cool off.
For the Besciamella:
Melt the 1/2 cup butter in a pan over medium heat. Stir in the flour with a wooden spoon. Cook's Note: This is an important moment, as you have to slowly toast the flour without burning it. This will help you lose the flowery taste.
Warm up the milk and gradually ladle into the pot with the butter-flour mixture, whisking constantly while bringing the mixture to a boil. Reduce the heat, and simmer for about 15 minutes. Season the sauce with freshly grated nutmeg, salt, and pepper.
Because you are working with pasta that does not require boiling, you have to make sure that there are no pieces of lasagne sticking out of the sauce because they won't cook.
When you decide to tap into your reserve of frozen lasagne, keep in mind you need to thaw the frozen lasagne overnight before reheating.
If the sauce is too thick, add a little more milk, if too runny, return to the heat and add a pat of butter mixed with an equal amount of all-purpose flour. The most important thing though is: Besciamella should not taste floury. If you think your sauce is ready, but you can spot a hint of "flouriness" when you taste it, think again, and keep on cooking it for a few minutes more.