Which French mother sauce is made from a white roux and milk?

The French mother sauce made from a white roux and milk is béchamel.

Béchamel combines butter and flour cooked into a pale roux with milk, producing a smooth white sauce. It is commonly seasoned with salt and nutmeg, and sometimes onion, bay leaf or thyme. The roux thickens the milk by releasing flour starch into the liquid, while gentle cooking gives the sauce a velvety texture.

A recipe resembling modern béchamel appeared in François Pierre de La Varenne’s Le cuisinier françois in 1651. The first clearly named béchamel sauce is generally associated with The Modern Cook by Vincent La Chapelle, published in 1733. The sauce later became one of the classic French mother sauces, a group used as foundations for many derivative preparations.

Béchamel is often confused with velouté. Both use a pale roux, but béchamel uses milk, whereas velouté uses a light stock. Hollandaise is emulsified from egg yolks and butter, and espagnole is a brown sauce based on brown roux and stock. Béchamel can become Mornay sauce when enriched with cheese, or serve as a base for gratins, croque monsieur and lasagne.