For the Bolognese Ragù:
Begin by composing the ragù, for it demands the longest, most patient simmer to reach perfection. Finely mince the carrot, celery, and onion to fashion a classic mirepoix, the aromatic foundation of Italian heritage. Dice the pancetta into exquisite, minute cubes, or mince it finely with a knife. In a spacious casserole dish (ideally crafted of terracotta or cast iron), warm a generous swirl of extra virgin olive oil. Introduce the pancetta, allowing it to render gently and release its rich virtues until lightly gilded and crisp. Add the minced aromatics and sweat over a gentle heat for 10-15 minutes, stirring reverently, until they are tender and translucent.
Now, introduce the minced meats. Sear them over a more spirited flame, breaking the crown of the meat apart with a wooden spoon, until it has assumed a rich, sealed color of roasted perfection. Deglaze the pan with red wine, allowing the spirited alcools to evaporate entirely into the ether. Strew in the double-concentrated tomato paste, stirring to dissolve its deep essence. Pour in the pureed tomatoes and warm, nurturing broth (or hot water). Season with salt and pepper to taste. Bring the ragù to an elegant simmer, then reduce the flame to its absolute minimum; cover, and allow the alchemy to unfold slowly for at least 2-3 hours (ideally 3-4 hours), stirring occasionally. The ragù must emerge thick and majestic. Should it dry during its long slumber, revive it with a touch more warm broth or water. Taste, and adjust the seasoning with salt and pepper before lifting it from the flame.

For the Béchamel:
While the ragù is deep in its slow reverie, turn your spirit to the creation of the béchamel. In a small saucepan, melt the butter over gentle heat. Withdraw the pan from the flame and introduce the flour all at once, whisking vigorously to forge a smooth, flawless paste known as a "roux". Return the pan to a low heat and toast the roux for a few moments, stirring continuously, without allowing it to take on color. Meanwhile, warm the milk in a separate vessel, stopping just short of a boil.
Pour the warm milk onto the roux in several stages, whisking with persistent vigor to banish any potential lumps. Bring the béchamel to a slow boil over gentle heat, stirring constantly, as it ascends to its velvet potential. As it begins to thicken, whisper the heat even lower and cook for 2-3 minutes until it attains the perfect density (it must be silky and enrobing, never watery). Season with salt and a generous rasp of freshly grated nutmeg. Remove from the fire and press plastic film directly onto the surface to prevent a skin from forming upon its smooth face.

For the Fresh Pasta:
Boil the spinach, squeeze out every drop of moisture with absolute care, and purée it in a mixer until perfectly smooth. Upon a wooden work surface, shape the flour into a majestic mound, creating a well at its heart. Crack the eggs into the center and add the vibrant spinach purée. With a fork, gently whisk the eggs and spinach, gradually carrying down the flour from the inner walls. As the mass gains body, begin to knead with your hands, working with vigor for about 10-15 minutes, until you obtain a smooth, elastic, and harmonious dough. Envelop the dough in plastic wrap and leave it to rest at room temperature for at least 30 minutes to ease its gluten tension.
Once rested, divide the dough into smaller portions. Lightly dust the board and each portion with flour. Sheet each portion with a rolling pin or a pasta machine, drawing out thin, delicate veils of pasta (about 1 mm thick). Cut these sheets into rectangles aligned with the dimensions of your baking dish. Bring a pot of lightly salted water to a boil; immerse the sheets one by one for 30-40 seconds, lift them with a skimmer, and transfer them to a dry cloth to gently blot away the water and lay them side by side.

For the Assembly and Baking:
Preheat the oven to 180°C (static). Generously butter the bottom and sides of an artisanal baking dish. Spread a thin, guiding layer of veloute-besciamella over the base. Lay down a sheet of fresh pasta (trimming it with care to fit the dish, if necessary). Drape the pasta in a luxurious layer of Bolognese ragù, followed by a ribbon of béchamel and a lavish snowfall of grated Parmigiano Reggiano.
Continue this ritual, alternating the layers with intent: pasta, ragù, béchamel, and Parmigiano. Carry on until all components have yielded their essence, crowning the final layer with béchamel and a magnificent dusting of Parmigiano Reggiano. You may dot the crown with a few pearls of butter to encourage a perfect, gilded gratin.
Bake the lasagne in the preheated oven for 30-40 minutes, until the top is beautifully gratinéed and the juices bubble merrily at the edges, singing of comfort. If the crust begins to color too quickly, gently shield it with foil during the final moments of baking.
Once fully realized, withdraw the lasagne from the oven and let it rest for at least 10-15 minutes before carving and presenting. This brief repose allows the flavors to settle into a harmonious whole and makes portioning an act of elegance.