Melt the butter in a saucepan and stir in the sifted flour to form a sticky paste.
Cook gently for a couple of minutes until it thickens slightly, then gradually add hot milk, stirring continuously to avoid clumps.
Season with salt, pepper, and nutmeg, then cook over medium-low heat until the sauce thickens, but be careful not to overcook it.
For the Lasagna
Assemble the lasagna: Take a baking dish with high sides and spread a layer of ragù and béchamel at the bottom.
Layer the pasta, ragù, and béchamel: Add the first layer of pasta, followed by another layer of ragù and béchamel. Continue layering until the dish is fully filled.
Top with Parmesan: Finish the lasagna with a generous sprinkle of grated Parmesan cheese.
Bake the lasagna: Bake the lasagna at 180°C (350°F) for about 30 minutes. The result will be a delicious and satisfying flavor triumph!