Lesson 1: Bechamel
Stir equal parts flour and butter in a hot skillet until it starts to smell toasty and turns light yellow. Meanwhile, have a pan of milk warming on a low flame. Maybe steep in a bay leaf, peppercorns, sliced shallot, or whatever you want, but you don’t have to. Add strained milk to the flour and whisk until it comes to a light boil and the chunks of roux dissolve. Simmer until thickened. Season with salt and pepper and maybe a pinch of nutmeg if you want.
Variations:
Mornay sauce: add a handful of shredded Compte/Gruyere and Parmesan.
Cream sauce: stir in some heavy cream. Duh.
Soubise: sauté some minced onions and purée. Stir in. A variation adds a bit of tomato paste.
Cheddar: add shredded cheddar cheese, ground mustard, and Worcestershire sauce. Good with macaroni.