In a medium saucepan, melt butter. Add flour and whisk until smooth. Cook for about 1-2 minutes over medium-low heat until smooth and bubbly. You want to cook out the raw flour taste, but don’t want the roux to brown. Carefully add the milk (all at once, or gradually, depending on milk temperature—see note), whisking constantly. Continue cooking, whisking, until the sauce is smooth, thick, and glossy, about 5 minutes. If not using immediately, remove from heat, transfer to a bowl, and place a layer of plastic wrap directly onto the surface of the sauce to prevent a skin from forming.

*Milk temperature can be a somewhat polarizing topic in béchamel preparation. (Google it—you’ll find a ton of opinions on the subject!) Some find that the smoothest sauces are created by adding cold milk to hot roux. Others hold with just as much conviction that warming the milk (to hot but not boiling) before adding it to the hot roux in one addition is best. Honestly, I think this comes down to personal preference and which method you were taught. I’ve used both with good results. Béchamel made with hot milk tends to thicken more quickly. To prevent lumping, cold milk needs to be added more gradually than hot milk, whisking until each addition is smooth. Regardless of milk temperature, I find that whisking constantly (and vigorously if you see any lumps forming as you’re adding the milk) is key. Try both methods and find which you like best!