This is the classic lasagna recipe, the same lasagna you would find on the table of many Tuscan and nothern Italian families for Sunday lunch or Holiday feasts.
In a pot, melt the butter and add the flour. Mix until you get a paste and cook it for a minute or two until it gets thicker.
Add the room temperature or warm milk and turn down the heat. Mix occasionally, to melt the roux and to make sure it doesn’t stick to the pot.
Let it simmer for 15-20 minutes until it gets thick enough to coat a spoon, then season with salt, black pepper and a pinch of ground nutmeg to taste.
Assemble the layers:
Preheat the oven at 200°C (400°F).
Spread a thin layer of white sauce on the bottom of the pan, cover with a layer of pasta, then a layer of Ragù sauce, a layer of bechamel sauce and grated Parmigiano.
Repeat the layers, pressing down a little bit when you add the pasta. When the pan is full, finish with a last layer of pasta, sauce and a generous amount of grated Parmigiano cheese.
Bake in the middle rack of the oven for about 35-40 minutes. If the crust is not crunchy enough, finish with 3-4 minutes under the broiler. If instead you notice the crust getting too brown before the cooking time is over, cover the pan loosely with foil.
Don't add too much sauce between layers. How much sauce? Not so much that everything floats; enough that every piece of pasta is completely moistened.
Choose a baking dish with tall edges to make sure everything fits!
Always start with a layer of sauce in the baking dish to prevent the pasta from sticking.
The edges should be bubbling and the top should be deeply golden. Insert a thin knife through the center; it should slide through the pasta without resistance.
After baking, let the lasagna rest before cutting it. I know it's difficult to wait, but let the lasagna rest for 10–15 minutes before cutting. Straight from the oven the sauces are still very loose; resting gives you much cleaner layers.Aim for at least 4-5 layers of pasta.