In case you were wondering (you’re probably not, actually, but I’m going to tell you anyway), this sauce is named after the Marquis de Béchamel. In Italian it’s called balsamella or besciamella. The original and full French version also involves steeping some onion and a bay leaf in milk for 30 minutes, to infuse the sauce with more flavor, but here’s an everyday approach. My simplified version is a snap to make and is perfect with my Baked Rigatoni. You could also use it the way you would hollandaise sauce.
In a 2-Quart Saucepan, melt the butter over medium heat. Add the flour and whisk until smooth, about 2 minutes. Gradually add the warm milk, whisking constantly to prevent any lumps from forming. Simmer over medium heat, whisking constantly, until the sauce is thick, smooth, and creamy, about 10 minutes (do not allow the béchamel sauce to boil). Remove from the heat and stir in ½ teaspoon of salt and a pinch each of white pepper and nutmeg. Season the sauce with more salt, pepper, and nutmeg to taste. (The sauce can be made up to 3 days ahead. Cool, then cover and refrigerate.)