he key to making this dish properly is making a loose béchamel sauce and partially cooking the pasta before finishing it in the béchamel. This way the pasta absorbs some of the sauce. The pasta is then removed from the heat before the cheese is added to prevent it from separating. For variations, see the Notes below. —woo wei-duan
Bring to a boil 7 litres of water with 3 tablespoons of salt in a large pot over high heat. Take a 11 x 14 inch rectangular baking pan and grease it with butter and sprin-kle it with 20 gms of breadcrumbs, shaking out any excess.
Meanwhile put 50 gms of butter and the flour in a large saucepan over medium heat and make a loose béchamel according to the directions here but using 1.25 litres of milk. Taste the béchamel and add salt, pepper, and nutmeg to taste. Cook the béchamel until it simmers and thickens, about 10 minutes after it begins to simmer. The béchamel needs to be thinner than usual because the pasta will finish cooking in the liquid and will absorb the extra liquid. Remove from the heat.
Add the macaroni to the boiling water and cook for half the amount of time indicated on the package. Drain the pasta and toss with the béchamel.
Stir to mix well and cook over medium heat for 3-4 minutes until the béchamel has been absorbed by the pasta.
Remove from the heat and add the cheeses. Do not leave the heat on or continue to heat the pasta or the sauce may separate.
Stir just until the cheese has melted.
Pour the pasta into the baking dish.
Sprinkle the remaining 20 gms of breadcrumbs over the top of the pasta. Cut the butter into thin pieces and dot the top of the breadcrumbs, spacing the butter evenly.
Bake in the oven for 20 minutes until the breadcrumbs are golden.
Variation 1: Skip preparing the pan for the oven, eliminate the breadcrumbs and butter and don't bake it. Just serve the pasta once the cheese has melted.
Variation 2: Add a clove of bruised garlic to the melted the butter when making the bechamel and discard it before adding the pasta.
Variation 3: Add 50 gms of cubed ham or thin slivers of prosciutto after the cheese melts.
Variation 4: Add 50 gms of blue cheese like Gorgonzola or Roquefort as part of the 225 gms of cheese.