Melt the butter on medium heat and add the sifted flour, whisk until you get the roux. Slowly add the warm milk and keep whisking to avoid lumps (they will melt anyway once it simmers).
Reduce to low heat and keep whisking until it starts simmering and becoming thicker. Add the salt, black pepper and ground nutmeg to taste. Once the sauce is thick enough to coat a spatula, turn off the heat and set aside.
Assembly
Boil the pasta in a large pot of salted water and drain 3-4 minutes before the normal cooking time.
If you want to layer it like a Lasagna, start coating the cocottes or a baking pan with a layer of Béchamel so the pasta won't stick. Add a layer of pasta, a layer of Ragù sauce, a layer of Béchamel and sprinkle with Parmesan. Repeat until you reach the top.
You can also decide to mix the pasta together in a bowl with the Béchamel, the Parmesan cheese and the Ragù sauce and then pour it in the cocottes.
In both cases, end with a layer of Béchamel and a generous sprinkle of Parmigiano cheese for a nice crust.
Bake in the oven at 370°F / 190°C for about 20 minutes. If needed, leave 2-3 minutes under the broiler to get the crispy crust.
Notes
What pasta format should I use?You can use any pasta format you prefer: short cuts like Penne, Fusilli, or Rigatoni, or long cuts like Spaghetti or Ziti. Follow the same recipe steps for any pasta format you choose to use.