Preheat the oven to 180°C (350°F).
Make the ragù: heat a large, heavy-based saucepan and add the chopped Pancetta with a little Olive oil and a knob of Unsalted butter. Cook until the pancetta has rendered its fat and begun to colour.
Add finely diced Onion, Carrot and Celery stalk and sweat gently until soft and translucent, about 8–10 minutes.
Increase the heat, add the Ground beef and brown it well, breaking up any lumps; season with Salt and Black pepper as it cooks.
Pour in the Dry white wine to deglaze the pan and let it reduce until mostly evaporated, then stir in the Tomato paste and cook briefly to concentrate the flavor.
Add the Beef stock and a splash of Whole milk, bring to a very gentle simmer, then reduce the heat and cook partially covered for at least 1–1½ hours (longer if you can) until thick, rich and deeply flavored. Adjust seasoning to taste.
Meanwhile make the béchamel: melt another knob of unsalted butter in a saucepan, whisk in the Plain flour to form a paste and cook for a minute or two. Gradually whisk in warm milk until smooth and simmer gently until the sauce coats the back of a spoon.
Season the béchamel with Fine salt and a generous grating of Nutmeg. Keep warm.
Assemble the lasagne: spread a thin layer of ragù in the base of a baking dish, top with a layer of Fresh spinach lasagne sheets (lasagne verdi), spoon over ragù, then a layer of béchamel and a scattering of grated Parmigiano Reggiano. Repeat to make 3–4 layers, finishing with béchamel and a generous dusting of Parmigiano; dot the top with a few small knobs of unsalted butter.
Bake for 30–40 minutes until the top is golden and the filling is bubbling through the layers.
Let the lasagne rest 10–15 minutes before slicing so the layers set. Serve warm with extra grated Parmigiano if desired.
