Brown 150g of diced pancetta in a little olive oil in a large pot. Cook 50g of finely chopped carrot, 50g of finely chopped onion, and 50g of finely chopped celery for 5-6 minutes. Add 300g of ground beef and brown it.
Pour in 120ml of red wine and let it evaporate completely. Stir in 300g of tomato passata and season with salt and pepper. Once boiling, simmer for at least 2 hours, adding hot vegetable broth a ladle or two at a time.
Meanwhile, wilt 250g of spinach in a covered pan with a little water. Drain, cool, squeeze dry, and blend to a purée.
Knead the spinach with 350g of fine durum wheat semolina, 150g of all-purpose flour, 2 eggs, and 3 egg yolks into a smooth dough. Wrap and rest for 30 minutes.
Roll the dough through a pasta machine, folding it at first, to about 0.02in / 0.5mm thick. Cut into 12 × 8in / 30 × 20cm sheets, blanch each in boiling salted water for 30-40 seconds, and pat dry on a cloth.
Melt 70g of butter and stir in 70g of all-purpose flour. Whisk in 1 liter of warm whole milk a little at a time and cook, stirring, until thick. Season with salt and nutmeg.
Preheat the oven to 325°F / 170°C. In a 12 × 8in / 30 × 20cm baking dish, layer béchamel, ragù, and some of 270g of grated Parmigiano Reggiano, then cover with pasta.
Repeat to make five layers, finishing with ragù, the remaining Parmigiano, and dots of butter. Bake for 40 minutes.
